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AMERICAN SCIENCE SERIES, ELEMENTARY COURSE

THE ELEMENTS

OF

CHEMISTRY

A TEXT-BOOK FOR BEGINNERS

BY

IKA REMSEN"

Professor of Chemistry in the Johns Hopkins University

NEW YORK
HEKRY HOLT AND COMPANY

1900.

<$*.

Copyright 1886,

BY

HENRY HOLT & CO,

48 6555

JUL 2 4 1942

K i

ROBERT DRUMMOND, PRINTER, NEW YORK.

PREFACE.

This book is written upon much the same plan as the
Briefer Course in the same series. It is, however, mate-
rially simpler in many parts, and is in every way better
adapted to younger pupils. In the opinion of the author
a rational course in chemistry, whether for younger or older
pupils, is something more than a lot of statements of facts
of more or less importance; a lot of experiments of more
or less beauty; or a lot of rules devised for the purpose of
enabling the pupil to tell what things are made of. If the
course does not to some extent help the pupil to think as
well as to see, to reason as well as to observe, it does not
deserve to be called rational. Not only must the pupil
perform experiments, but he must know why he performs
them, and what they teach. A good plan to follow is to
talk over a certain part of the subject, showing how to con-
struct the apparatus necessary for some of the experiments,
and stating in a general way what is to be learned; then to let
the pupil perform the experiments with the aid of the book
and the teacher; and afterwards to make the experiments
the basis for questioning. In this way the pupil will be-
come observant, and at the same time he will discover when
his experiments have been performed in the wrong way.
It is better to go slowly at first so as to allow the pupil
time to become familiar with his surroundings and to enable

IV PREFACE.

him to learn how to work at the laboratory desk. A badly
constructed piece of apparatus or an experiment badly per-
formed in any way should not be allowed to pass. Experi-
ments should be repeated as many times as may be neces-
sary to secure accurate work.

Chemical theories are treated in a subordinate way, as it
is believed that the attention should first be directed to the
simpler facts of the subject and the methods by which these
facts are learned. A brief statement of a few of the pre-
vailing hypotheses is given in Chapter XIV. Whether it
will be advisable for the pupils to spend any time in study-
ing this chapter will depend upon their age and their men-
tal attainments. If all they can do is to learn the statements
by heart and repeat them without showing any signs of
comprehension, then unquestionably the chapter should be
omitted. It should be remembered that the object of the
course laid down in this book is not to make chemists, but
to help to develop sound minds, and at the same time to
awaken interest in a set of natural phenomena of great im-
portance to mankind. It is quite possible to teach the sub-
ject in such a way as to destroy all interest in chemical
phenomena and to make the pupil shudder whenever a chemi-
cal formula is mentioned. There is no better way to accom-
plish the latter result than by giving prominence to incom-
prehensible theories and forcing the pupils to master a lot
of equations which represent facts of which they are entirely
ignorant.

Baltimore, December 27, 1886.

CONTENTS.

CHAPTER I.

PAGE

Chemical Changes— Physical Changes ...... . . 1

CHAPTER II.
The Chemistry of the Air 16

CHAPTER III.
Oxygen c . . . &1

CHAPTER IV.
Combining Weights 31

CHAPTER V.
Nitrogen 37

CHAPTER VI.
Water 41

CHAPTER VII.
Hydrogen 45

CHAPTER VIII.
Water (continued) 53

CHAPTER IX.

Compounds of Nitrogen with Hydrogen and Oxygen .... 66

CHAPTER X.

Chlorine and Its Compounds with Hydrogen and Oxygen. . . 77

VI CONTENTS.

CHAPTER XL

PAGE

Acids—Bases — Neutralization— Salts 88

CHAPTER XII.
Carbon 95

CHAPTER XIII.

Compounds of Carbon with Hydrogen, with Oxygen, and with

Nitrogen 106

CHAPTER XIV.

Atomic Theory— Atomic Weights— Molecular Weights— Valence

— Classification of the Elements 0 124

CHAPTER XV.
The Chlorine Family: Chlorine, Bromine, Iodine, Fluorine. . 132

CHAPTER XVI.
The Sulphur Family: Sulphur, Selenium, Tellurium .... 139

CHAPTER XVII.

The Nitrogen Family: Nitrogen, Phosphorus, Arsenic, and Anti-
mony—Boron and Silicon 15!

'

CHAPTER XVIII.
Base-forming Elements — General Considerations 161

CHAPTER XIX.
The Potassium Family: Potassium, Sodium, (Ammonium) . . 165

CHAPTER XX.

The Calcium Family: Calcium, Barium, Strontium < . 0 . 178

CHAPTER XXI.

The Magnesium Family: Magnesium, Zinc, Cadmium— The

Copper Family: Copper, Mercury, Silver 185

CONTENTS. VH

CHAPTER XXII.

PAGE

The Aluminium Family — The Iron Family: Iron, Cobalt,

Nickel 196

CHAPTER XXIII.
Manganese— Chromium— Uranium — Bismuth 206

CHAPTER XXIV.
Lead—Tin— Platinum— Gold 209

CHAPTER XXV.
Some Familiar Compounds of Carbon 216

CHAPTER XXVI.
Other Compounds of Carbon 231

APPAKATUS AND CHEMICALS.

For the benefit of those who have no laboratory at
command, and who may wish to make arrangements for
going through with the experimental work, the following
list has been drawn up. In it is included everything
necessary to perform the experiments on a small scale.
Should it be desired to fit up a room with conveniences for
students, the amount of apparatus necessary would depend
upon the number of students, but for each individual the
expense would be small, as many of the pieces of apparatus,
such as the galvanic battery, burette, weights, scales, etc.,
need not be multiplied. In place of some of the pieces of
apparatus described in the book, ordinary kitchen utensils
will answer: thus, for example, instead of the trough for
collecting gases, a tin pan or a deep earthenware dish may
be used; instead of the water-bath, a stew-pan, fitted with
two or three different-sized tin or sheet-iron rings; and in
place of glass cylinders for working with gases, wide-
mouthed cheap bottles.

The publishers do not deal in chemicals and apparatus,
nor, they may as well say, receive commissions on them.
Any orders should be sent direct to the dealers.

Messrs. Eimer & Amend, Nos. 205 to 211 Third Avenue,
New York, whom the publishers take the responsibility of
recommending as thoroughly reliable, will furnish each of
the following articles at the price given.

If several pieces of the apparatus in List No. 1 are taken,
a discount of 10 per cent will be made; on a complete set
20 per cent discount will be allowed; on three or more sets,
25 per cent.

One or more of the articles in List No. 2, if not marked
"net" or "20 per cent," will be supplied at 25 per cent
discount if ordered with sets of the apparatus in List No. 1.

A discount of 10 per cent will be given on a complete
set of the chemicals, and of 15 per cent on three or more
sets.

APPABATUB AJ3D CEBM1CALS.

IX

For most items less than the whole set, there will have
to be a small additional charge for packing. It should be
realized, however, that usually the charge for packing one
article must be as large as for several. Some articles can,
of course, be mailed without any charge for packing.

List No. 1.

A list of apparatus and chemicals necessary for performing all of
uhe experiments in Remsen's Elements of Chemistry, with the excep-
tion of experiments Nbs. 34, 36,
113. To perform ther~
List No. 2 is required.

A list ol apparatus and chemicals u
the experiments in Remsen's Elements oi ^ut
tion of experiments Nbs. 34, 36, 46, 47, 48, 49, 51, 65, 66, 79, 80, and
113. To perform these latter experiments, the apparatus given in

APPARATUS.

1 Nest Beakers, 1-3 $0 40

1 Jeweller's Blowpipe, 8 in 15

7 Wide-mouth Flint Bottles, two

each, 2, 4, 8 oz., and one 32 oz. 50
1 Bunsen's Burner with regula-
tor, or 6 oz. glass alcohol

lamp, same price 50

1 5-in. U-tube 25

2 doz. Assorted Corks 20

1 Nest Hessian Crucibles,

"threes" ... 6

1 1^4 -in. Porcelain Crucible 18

1 25 CC Grad. Cylinder 50

1 Deflagrating Spoon 25

1 each Evaporating Dish, 23^

and 3^ in 40

1 Lead Dish, 2 in 25

1 Round File, 5 in 25

1 Triangular File, 5 in 25

1 Pack White Filters, 4 in ....... . 12

4 Flasks: one 4 oz., two 8 oz.,

oriel6oz 80

1 SteelForceps 20

2 Funnels, 2^ in 24

2 Funnel Tubes, one 10 in. , one

15 in . . 35

1 Gas Bottle, 8 oz., with 2-hole R

Stopper 40

*4 lb. Assorted Glass Tubing, 4-7 15

2 Sheets each Red and Blue Lit-

mus-paper 20

1 Horseshoe Magnet, 3 in 20

1 Porcelain Mortar and Pestle,

3^ in 45

1 Piece Platinum Foil, lxl ^ in. . 60

6 in. Medium Platinum Wire 20

1 Plain Retort, 8 oz 30

1 Stoppered Retort, 16 oz 55

3 ft. Rubber Tubing for gas, ^ in. 39
(Only needed if Bunsen's Burner

is used.)

2 ft. Rubber Tubing (for connec-

tions) 20

1 %\i in. Sand Bath $0 15

1 Hand Scale, with weights 85

1 Test Tube Stand 30

12 Test Tubes, 5 in 30

1 Test Tube Brush 5

1 Test Tube Clamp 20

1 Iron Tripod 30

2 2-in. Watch-glasses 10

1 5-in. Water-bath. 1 00

2 Wire Clamp Supports 2 00

$14 74
CHEMICALS.

4 oz. Acid Acetic, pure (bottle 5

cents extra) $0 10

4 oz. Acid Arsenious ... 10

16 oz. " Hydrochloric (bottle

15 cents extra). 10

8 oz. Acid Nitric (bottle 12 cents

extra) 10

2 oz. Acid Oxalic 10

16 oz. " Sulphuric (bottle 12

cents extra) 10

1 oz. Acid Tartaric 10

2 oz Alcohol, for experiments

only (bottle 4 cents extra). . . 10

8 oz. Alum 10

4 oz. Ammon. Chloride 10

8 oz. " Hydrate, concen-
trated (bottle 10 cents extra) 10

4 oz. Ammon. Nitrate ... 10

2 oz. Antimony, powdered 10

2 oz " and Potassium

Tartrate 20

2 oz. Barium Chloride 10

4 oz. Calcium Chloride, fused. .. 10

4 oz. " Sulphate 10

4 oz. Carbon Disulphide (bottle

5 cents extra) 10

8 oz. Animal Charcoal, powdered 10

8 oz. Copper Foil 30

4 oz. k* Sulphate 10

1 oz. " Oxide... 15

4 oz. Fluorspar, powdered 10

APPARATUS AND CHEMICALS.

1 oz. Indigo. $0 10

1 oz. Iodine (bottle 2 cents ex-

tra) 40

4 oz. Iron Filings, fine ,.. 10

8 oz. " Sulphide 10

4 oz. " Sulphate 10

4 oz. Lead Sheet 10

4 oz. " Acetate 10

2 oz. " Nitrate 10

1 oz. " Peroxide 10

2 oz. " Sesquioxide 10

1 oz. Litmus 10

^ dram Magnesium Ribbon 20

1 lb. Manganese Dioxide, pow-
dered 10

1 oz. Mercury Red Oxide ]0

1 oz. Nutgalls, powered 10

2 oz. Parafflne 10

1 oz. Phosphorus (hot. 10c. extra) 15

1 dram Potassium ... 50

2 oz. " Bromide 10

4 oz. " Carbon, (bot.

5 cents extra) 10

4 oz. Potassium Chlorate $0 10

4 oz. " Dichromate 10

2 oz. " Ferrocyanide .. 10
4 oz. " Hydrate Sticks

(bottle 5 cents extra) 20

1 oz. Potassium Iodide (bottle 5

cents extra) 30

4 oz. Potassium Nitrate 10

2 oz. *' Permanganate. 10

1 dram Sodium (bot. 3c. extra). . 10

2 oz. ** Acetate 10

2 oz. " Bicarbonate..... 10

4 oz. " Biborate (Borax) 10
4 oz. *4 Hydrate (bottle

5 cents extra) 20

4 oz. Sodium Nitrate 10

4 oz. " Sulphate 10

8 oz. Sulphur, roll 10

4 oz. Tin, granulated 10

16 oz. Zinc, granulated...., 30

2 oz. " Sulphate 10

$8 00

List No. 2.

In order to perform experiments Nos. 34, 36, 46, 47, 48, 49, 51, 65,
66, 79, 80, and 113, the following additional apparatus is necessary:

2 Qt. Bunsen's Cells $3 00

2 Platinum Plates, lx^ inch 40

1 Charcoal Furnace,18in.(20p.c), 2 00

or 1 Charcoal Furnace, 24 in.,

$3 00(20p.c.);orl 10 burnerGas

Combustion Furnace $20 00

1 25-in. hard Glass Tube, 1 in. bore

(net) 1 00

or 1 25-in. Porcelain Combus-
tion Tube, 1 in. bore.. ..$1 75

3 pt. Woulff's Bottles, 2-necked. . 1 95
1 hard Glass Tube, drawn out,

12x^jin. bore 25

1 Oxyhydrogen Blowpipe $6 00

2 Gasholders for Oxygen and Hy-

drogen, 5 gal 26 50

1 Liebig's Condenser, 15 in 1 50

1 Burette, 50 c.c. f0 1 70

1 Pinchcock 25

1 Copper Air-bath, 6x8 in 5 00

1 Kellog-Bunsen's Vapor Lamp,
complete (a substitute in case
gas is not used as fuel) (net).. 10 00

$59 55

THE ELEMENTS OF CHEMISTRY.

CHAPTER I.
CHEMICAL CHANGES— PHYSICAL CHANGES.

Some Familiar Changes. — You are all familiar with
many changes which are taking place in the things around
you. Take, for example, the changes which are called
fire. You see substances destroyed by fire. They disap-
pear. You feel the heat produced by the burning. You
know that some things will burn and others will not.
Again, you all know that iron when exposed to the air is
changed, becoming covered with a reddish-brown substance
called rust. If fruit- juices or milk be allowed to stand in
contact with the air they become sour. If a spark comes
in contact with gunpowder there is a flash and the powder
disappears, dense smoke appearing in its place.

Changes of Another Kind. — If a piece of stone or of iron
be brought in contact with something hot it becomes hot
itself. If taken away it becomes cool again. If heated
very hot it gives light. When, for example, iron becomes
" red-hot" we can see it in a dark room. Iron may also
be changed by contact with loadstone. After it has been
rubbed with loadstone it has the power to attract and hold
to itself other pieces of iron. When a solid body is struck

2 THE ELEMENTS OF CHEMISTRY.

with another solid a sound is produced. At a low temper-
ature water is solid, forming ice. If the ice becomes warm
enough, it melts and becomes water. If the water is
heated enough it becomes steam. By cooling steam it
changes to water, and by cooling water it changes to ice.

Two Kinds of Change. — When a substance burns it be-
comes something entirely different. Iron-rust is not iron.
Sour milk is not fresh milk. Gunpowder after the flash
is not gunpowder. In these cases, then, the substances
which are changed disappear and something else is formed
in their place. On the other hand, when a piece of iron
which is hot is allowed to cool it is the same thing that it
was before it was heated. Eed-hot iron soon ceases to
give light if it is taken away from the fire. Water may
be cooled down and changed to ice, and the ice heated and
changed to water; and the water formed from the ice is
exactly the same thing as the water from which the ice
was formed. In these cases the substances are not per-
manently changed. You see thus that we have two classes
of changes presented to us for study:

1st. Those which do not affect the composition of sub-
stances.

2d. Those which affect the composition of substances
and give rise to the formation of new substances with
new properties.

Changes of the first kind are called physical changes.
Those of the second kind are called chemical changes.

Physics and Chemistry. — That branch of knowledge which
has to deal with physical changes is known as physics f
and that which has to deal with chemical changes is
known as chemistry. Everything that has to do with
motion, with heat, light, sound, electricity, and magnet-

CHEMICAL CHANGES— PHYSICAL CHANGES, 3

ism, is studied under the head of Physics. Everything
that has to do with the composition of substances and
changes in the composition is studied under the head of
Chemistry.

All Physical and Chemical Changes are Related. — Al-
though at first sight the different kinds of change already
mentioned appear to be quite distinct from one another,
they are in reality closely related. If a body in motion be
stopped suddenly it becomes hot. Many examples of a
similar change of motion into heat are familiar : a wire
becomes hot when hammered on an anvil ; a coin rubbed
on cloth becomes hot. In both cases the cause of the heat
is the interference with the motion. The hammer is
stopped and becomes hot ; the coin is not stopped, but the
motion is interfered with, and we have to push harder in
order to move it over the cloth than we should to move it
in the air. Again, we know that by means of heat we can
produce motion. The steam-engine is the best example of
this. We build a fire ; this heats the water in the boiler ;
the water is converted into steam, which expands and
moves the piston, and the motion of the piston is the seat
of all the complex motions which are found in the different
parts of the engine. The train or ship moves. What
moves it ? Plainly, the heat is the cause of the motion.
But we can go a step farther back and ask what causes the
heat. The answer is clear. It is the burning of the fuel.
But, in burning, the composition of the fuel is completely
changed. A. change is produced which is not heat. When
a piece of coal burns, then, its composition is changing,
and as a result of this change heat is produced. The heat
is, therefore, produced by a chemical change in the coal,
and we may say that the motion of the steam-engine is the

4 THE ELEMENTS OF CHEMISTRY.

result of the chemical change taking place in the coal or

wood which, in burning, produces the heat

Heat Causes Chemical Change. — Just as chemical change

produces heat, as in the burning of a piece of wood, so

heat causes chemical changes.

Experiment 1. — In a clean, dry test-tube put enough white
sugar to make a layer i to i inch thick. Hold the tube in
the flame of a spirit-lamp or a laboratory ourner
as shown in the figure. What changes take
place ? What do you notice on the sides of the
tube ? What remains behind ? What is its color
and taste? Does it dissolve in water? Is it
sugar? Is the change which has taken place
chemical or physical ? What caused it ?

Experiment 2. — From a piece of glass tubing
of about J inch internal diameter cut off a
piece about four inches long by making a martf
across it with a triangular file, and then seizing
it with both hands, one on each side of the
mark, pulling and at the same time pressing
Fig. i. slightly as if to break it. Clean and dry it,

and hold one end in the flame of a laboratory burner until it melts
together. During the melting twirl the tube constantly between
the finger and thumb so that the heat may act uniformly upon it.
After it has cooled down put into it enough red oxide of mercury
(mercuric oxide) to form a layer \ inch thick. Heat the tuDe as
in the last experiment. — What change in color do you notice?
What is deposited on the sides of the tube ? During the heating
insert a splinter of wood with a spark on the end into the tube.
What follows? Take it out and put it back a few times. Is
there any difference between the burning in the tube and out of
it ? What difference ? How do you know that the red substance
which you put into the tube has been changed ? Is the change
chemical or physical ? What caused the change ?

Chemical Change Caused in Other Ways. — In the two

experiments just performed heat caused chemical change.
Chemical changes can be produced in other ways. The
simplest way is by bringing substances together.

CHEMICAL CHANGES— PHYSICAL CHANGES

Experiment 3. — Examine a piece of calc-spar or marble.
Notice whether it is hard or soft. Heat a small piece in a glass
tube snch as used in Experiment 2. Does it change in any way ?
Does it dissolve in water? In order to learn whether a substance
is soluble in water proceed as follows : Put a piece about the size
of a pea in a test-tube with distilled water. Thoroughly shake, and
then, as heating usually aids solution, boil. Now pour off a few
drops of the liquid on a piece of platinum-foil* or a watch-glass,
and by gently heating cause the water to pass off as steam. If
there is anything solid in solution there will be something solid
left on the platinum-foil or watch-glass. If not, there will be
nothing left. — Knowing now the general properties of the calc-
spar or marble you will be able to determine whether it is
changed or not. Treat a small
piece with dilute hydrochloric
acid. What takes place? After
the action has continued for
about half a minute insert a
lighted match in the upper part
of the tube. Does the match
continue to burn ? Does the sub-
stance in the tube burn ? Is the
invisible substance in the upper
part of the tube ordinary air?
Why not? Does the solid sub-
stance disappear ? In order to tell
whether it has been changed
chemically the hydrochloric acid Fig. 2.

must be gotten rid of. This can be done by boiling it, when
it passes off in the form of vapor, just as water does, and then
whatever is in solution will remain behind. For this purpose put
the solution in a small, clean porcelain evaporating-dish, and put
this on a vessel containing boiling water, or a water-bath. The
operation should be carried on in a place where there is a good
draught, so that the vapors will not collect in the working-room.
They are not poisonous, but they are annoying. The arrange-

* The expensive metal platinum is much used in chemical labora-
tories, for the reason that it resists the action of heat and of most
substances.

6 THE ELEMENTS O^BSEMISTBY.

ment for evaporating is illustrated in Fig. 2. After the liquid
has evaporated and the substance in the evaporating-dish is dry,
examine it and carefully compare its properties with those of the
substance which was put into the test-tube. Is it the same sub-
stance ? Is it hard or soft ? Does it change when heated in a
tube? Is there an appearance of bubbling when hydrochloric
acid is poured on it ? Does it dissolve in water ? Does it change
when allowed to lie in contact with the air ?

Experiment 4. — Bring together in a test-tube a small piece
of copper and some moderately dilute nitric acid. Hold the
mouth of the tube away from your face and do not inhale the
vapors. What is the appearance of the vapors given off ? What
is the appearance of the liquid in the tube ? Does the copper dis-
solve ? Examine the solution, as in the preceding experiment,
and see what has been formed. What are the properties of the
substance found after the liquid has evaporated ? Is it colored ?
Is it hard or soft ? Does it change when heated in a tube ? Is it
soluble in water ? Does it in any way suggest the copper with
which you started ?

Experiment 5. — Try the action of dilute sulphuric acid on a
little zinc in a test-tube. An invisible gas will be given off.
Apply a lighted match to the mouth of the tube. What takes
place ? After the zinc has disappeared evaporate the solution as
before. Carefully compare the properties of the substance left
behind with those of zinc.

Experiment 6.— Hold the end of a piece of magnesium rib-
bon about eight inches long in a flame until it takes fire. Then
hold the burning substance quietly over a piece of dark paper, so
that the light, white substance which is formed may fall upon the
paper. Compare the properties of this product with those of
magnesium.

Experiment 7. — In a small dry flask of about four ounces
capacity put a bit of granulated tin or of pure tin-foil. Pour
upon it enough concentrated nitric acid to cover it. If no change
takes place at first, heat gently, and presently you will have
evidence that change is taking place. Is there anything in this
experiment whio^ suggests Experiment 4 ? What is left behind
after the action is finished? Compare the properties of the
product with those of tin.

CHEMICAL CHA^Fm—PHYSICAL CHANCES. 7

Solution Aids Chemical Action. — In the cases just studied
it was only necessary to bring the substances together,
when they acted at once. In each case one of the sub-
stances used was a liquid. Solids do not, as a rule, act
upon one another as re^ily as liquids act upon solids, for
the reason. that the small particles of which the solids are
made up cannot be brought as closely together as the par-
ticles of liquids.

Experiment 8. — Mix together in a dry mortar a little dry
tartaric acid and about an equal quantity of dry bicarbonate of
soda (sodium bicarbonate). Do you see any evidence of action ?
Now dissolve a little tartaric acid in water in a test-tube, and a
little carbonate of soda in water in another test-tube. Pour
the tv/o solutions together. What evidence have you now that
action takes place ? Pour water upon the dry mixture first made.
Does action take place? What causes the bubbling? Will a
match burn in the gas ? In which experiment already performed
was a similar gas obtained ?

Experiment 9. — Mix together in a dry mortar a little dry
sulphate of iron (green vitriol) and a little dry ferrocyanide of po-
tassium (yellow prussiate of potash). Does action take place?
Make a solution of each of the two substances and pour them
together. What evidence have you that action takes place?
I^our water on the dry mixture. Does action take place ?

Summary. — From the experiments it will be seen (1) that
heat causes chemical change; (2) that in some cases simple
contact of substances is sufficient to cause chemical change;
(3) that solution aids chemical change. In all the cases
of chemical action thus far studied one thing was observed,
viz.,, that the substances which were acted upon lost their
own properties and new substances were formed. This
^true in all cases of chemical action, and the truth maybe
stated thus:

Whenever two or more substances act upon one another

8 THE ELEMENTS OF CHEMISTRY.

chemically they lose their own properties, and new sub-
stances are formed with entirely different properties.

Difference between Combining Chemically and simply
Mixing. — By mixing is meant bringing things together
closely, so that the particles of on^ehall be in contact with
the particles of the other. We mix salt and sugar by put-
ting them together in a vessel and shaking them, or by
stirring as with a pestle in a mortar. The longer we stir
the more closely the substances are brought together. But
no matter how long we may stir the mixture, it remains a
mixture and contains both sugar and salt. In some cases,
by stirring, chemical action can be brought about, but
generally not.

Experiment 10. — Mix two or three grams of powdered roll-
sulphur and an equal weight of % very fine iron filings in a small
dry mortar. Examine a little of the mixture with a microscope.
Can you distinguish the particles of sulphur and those of iron ?
Pass a small magnet over the mixture. Are particles of iron
drawn out of the mixture ? Has chemical action taken place ?

Experiment 11. — Pour two or three cubic centimetres of
bisulphide of carbon on a little powdered roll-sulptor in a dry test-
tube. Does the sulphur dissolve ? Treat iron filings in the same
way. Does the iron dissolve ? Now treat a small quantity of the
mixture prepared in Experiment 10 with bisulphide of carbon.
After the sulphur is dissolved pour off the solution in a good-
sized watch-glass and let it stand. Examine what is left in the
test-tube. Is it iron ? After the liquid has evaporated examine
what is left on the watch-glass. Is it sulphur ?

Experiment 12. — Mix three grams of finely powdered roll-
sulphur and three grams of fine wrought-iron filings or pow-
dered iron to be had of the druggists. Put the mixture in a
dry test-tube. Heat gently at first and notice the changes. At
first the sulphur melts and becomes dark-colored. It may even
take fire. But soon something else takes place. The whole mass
begins to glow, and if you at once take the tube out of the flame
the mass will continue to glow, becoming brighter. This will

CHEMICAL CHANGES— PHYSICAL CHANGES. 9

soon stop; the mass will grow dark and gradually cool down.
As soon as it reaches the ordinary temperature, break the tube
and put the contents in a mortar. Does the mass look like the
mixture of sulphur and iron with which you started ? An exam-
ination with the microscope, the magnet, and bisulphide of car
bon will prove that, while there may be a little iron left and pos-
sibly a little, sulphur, most of the bluish-black mass is neither
iron nor sulphur, but a new substance with properties quite dif-
ferent from those of iron and of sulphur.

What has Become of the Iron and the Sulphur ? — In the

last experiment a new substance was formed by the action
of sulphur upon iron. Neither substance has been de-
stroyed, but both hayo combined in a much more intimate
way than when they were simply mixed together. This
kind of combination which causes the properties of the
combining substances to disappear is called chemical com-
bination. Nothing is lost in the act, as has been shown by
weighing the substances before and after action.

Mechanical Mixtures and Chemical Compounds. — In a
mixture the substances are unchanged. They exist side by
side. In a chemical compound the substances ivhich are in
combination are completely changed. They are so intimate-
ly combined that they cannot be recognized by any ordinary
means.

Compounds and Elements. — Most of the substances found
in nature are made up of several others. Wood, for exam-
ple, is very complex, containing a large number of distinct
substances intimately mixed together. Some of these can
be got out separately, but it is impossible to get them
all out separately with the means at present at our com-
mand. Most of the rocks met with, and the different kinds
cf earth, as clay, sand, etc., are also quite complex, and it
is in most cases difficult to get out the substances contained

10 THE ELEMENTS OF CHEMISTRY.

in them. By proper methods, however, it is possible to
decompose the complex substances found in nature so as to
get simpler ones, and these again can usually be decom-
posed into still simpler ones which cannot be decomposed
by any means known to us. Substances which we cannot
decompose into simpler ones are called elements. Now, al-
though there are thousands and thousands of different
kinds of substances met with in nature, these are really
made up of a comparatively small number of simple sub-
stances or elements. The number of elements thus far
discovered is between sixty and seventy, but the larger
number of these are rare, and we might have a very ex-
cellent knowledge of the essentials of chemistry without
any knowledge of these rare elements. We shall find that
most things we have to deal with are really made up of
about a dozen elements, and that most of the chemical
changes which are taking place around us, and which we
need to study in order to get an insight into the nature of
chemical action^ take place between this small number of
elements.

An element is a substance which we cannot decompose into
simpler substances.

A compound is a substance ivhich can be decomposed into
simpler ones. A compound contains two or more elements
held together chemically.

Examples of Elements and Compounds. — As examples of
elements may be mentioned iron, copper, tin, silver, gold,
(sulphur, and lead. As stated in the last paragraph, they
are called elements for the reason that they cannot be de-
composed into simpler substances. Among familiar com-
pounds may be mentioned water, common salt or sodium
chloride, blue vitriol or copper sulphate^ chlorate of potash

CHEMICAL CHANGES-PHYSICAL CHANGES, 11

or potassium chlorate, marble or calcium carbonate, sand
or silicon dioxide. Each of these compounds consists of
two or more elements held together in chemical combina-
tion. Water can be decomposed by various methods into
two substances known as hydrogen and oxygen, and the
sum of the weights of the hydrogen and oxygen obtained
from a given weight of water is exactly equal to the weight
of the water decomposed. Sodium chloride can be decom-
posed into the two elements sodium and chlorine, and the
weight of the sodium added to the weight of the chlorine
exactly equals the weight of the sodium chloride. On the
other hand, the composition of an element cannot be
changed without adding something to it.

Chemical Action. — Just as the earth attracts all bodies
to it in some mysterious way which we call gravitation,
just as the magnet attracts pieces of iron, so substances are
drawn together chemically and, if they come in contact
under the proper conditions, chemical action takes place.
By this is meant that some change in composition is brought
about ; that the substances which are brought together dis-
appear and new ones make their appearance. But the
quantity of matter remains the same. The elements ar-
range themselves differently.

Three Kinds of Chemical Action. — The numerous cases
of chemical action may be divided into three classes: (1)
combination; (2) decomposition ; and (3) double decompo-
sition or metathesis. As an example of combination the
case of the action of iron on sulphur may be taken. The
two elements combine directly, forming a compound known
as iron sulphide. The action may be represented thus:
Iron + Sulphur — Iron Sulphide.

A good example of decomposition is that of the action of

12 THE ELEMENTS OF CHEMISTRY.

heat on the red oxide of mercury or mercuric oxide (see
Experiment 2). When this substance is heated two things
are obtained from it: an invisible gas, oxygen, which passes
out of the vessel and which can be detected by the fact that
substances burn in it more readily than they do in air ;
and a silvery-looking liquid, which is quicksilver or mer-
cury. The action in this case may be represented thus:

Mercuric Oxide = Mercury + Oxygen.

In double decomposition two or more substances act upon
one another and give rise to the formation of two or more
new ones. Thus when hydrochloric acid acts upon marble
(see Experiment 3) two substances, calcium chloride and
carbonic acid, are formed. This may be represented thus:

Hydrochloric Acid + Calcium Carbonate (or marble) =
Calcium Chloride + Carbonic Acid.

Most cases of chemical action which we have to deal with
are of the third kind.

The Cause of Chemical Action. — It is evident from what
we have already learned that there is some power which
can hold substances together in a very intimate way, so in-
timate that we cannot recognize them by ordinary means.
We do not know what causes sulphur and iron to combine,
but we know that they do combine. Similarly, we do not
know what causes a stone thrown in the air to fall back
again, but we know that it falls back. It is true we say
that the cause of the falling of the stone is the attraction of
gravitation, but this does not give us any information, for,
if we ask what the attraction of gravitation is, we can only
answer that it is that which causes all bodies to attract one
another. So, too, we may say that the cause of the chemi-
cal union of substances is chemical attraction. But in so

CHEMICAL CHANGES-PHYSICAL CHANGES. 13

doing we are only giving a name to something about which
we know nothing except the effects which it produces.

Importance of Chemical Action. — If this power, what-
ever it may be, should cease to operate, what would be the
result? As far as we can see all substances known to be
chemical compounds would be decomposed into the elements
of which they are composed, and there would be only about
sixty or seventy different kinds of substances. All living
things would cease to exist, and in their place we should
have three invisible gases and something very much like
charcoal. Mountains would crumble* to pieces, and all
water would disappear giving two invisible gases. The
processes of life in its many forms would be impossible.
These considerations will suffice to show the great impor-
tance of the subject of chemistry, and how impossible it
is without some knowledge of this subject to form any
conception in regard to the most important phenomena of
the universe.

Occurrence of the Elements. — As has already been stated
(p. 10), not more than a dozen elements enter largely into
^he composition of the earth. It has been estimated that
the solid crust of the earth is made up approximately as
represented in this table:

Oxygen 44-48 per cent.

Silicon 22-36 "

Aluminium. 6-10 "

Iron ^ 2-10 ' *

Calcium 1-7 "

Magnesium 0.1- 3 "

Sodium 2- 3 "

Potassium 1.5-3 "

While oxygen forms a large proportion of the solid crust
of the earth, it forms a still larger proportion (eight ninths)

14 THE ELEMENTS OF CHEMISTRY.

of water, and about one fifth of the air. Carbon is the
principal element entering into the structure of living
things, while hydrogen, oxygen, and nitrogen also are
essential constituents of animals and plants. Nitrogen
forms about four fifths of the air.

The Names of the Elements.— The names of the elements
are formed in many different ways. The name chlorine is
derived from a Greek word meaning greenish yellow, as this
is the color of chlorine. Bromine comes from a Greek word
meaning a stench, a prominent characteristic of bromine
being its bad odor. Hydrogen is formed from two Greek
words, one of which means water and the other to produce,
signifying that it enters into the composition of water.
Potassium is an element found in potash, and sodium is
found in soda„

The Symbols of the Elements. — It is convenient to use
abbreviations for the names of the elements and com-
pounds. Thus, instead of oxygen we may write simply 0,
for hydrogen E, for nitrogen N, etc. Very frequently the
first letter of the nam? of the element is used as the symbol.
If the names of two or more elements begin with the same
letter, this letter is used, but some other letter of the name
is added. Thus, B is the symbol of boron, Ba of barium,
Bi of bismuth, etc. In some cases the symbols are de-
rived from the Latin names of the elements. Thus, the
symbol of iron is Fe, from fer rum, ; of copper, Cu, from
cuprum ; of mercury, Hg, from hydrargyrum, etc. The
symbols of the more common elements will soon become
familiar by use. It is not desirable to attempt to commit
them to memory at this stage.

List of the Elements and their Symbols. — In the table
here given the names of those elements which are most

CHEMICAL CHANGES-PHYSICAL CHANGES. 15

widely distributed, and which form by far the largest part
of the earth, are printed in small capitals. The names
of those which are very rare are printed in italics.

Aluminium Al

Antimony Sb

Arsenic As

Barium Ba

Bismuth Bi

Boron B !

Bromine Br

Cadmium Cd I

Ccesium Cs j

Calcium Ca I

Carbon C

Cerium Ce I

Chlorine CI |

Chromium Cr

Cobalt Co

Columhium Cb

Copper Cu

Didumium Di

Erbium E

Fluorine F

Gallium Ga j

Glucinum Gl i

Gold Aul

Hydrogen H

Indium In

Iodine I

Iridium Ir

Iron Fe

Jjanthanum ... . . .La

Lead Pb

Lithium Li

Magnesium Mg

Manganese Mn

Mercury Hg

Molybdenum Mo

Nickel Ni

Niobium . Nb

Nitrogen N

Osmium . . . Os

Oxygen O

Palladium........ Pd

Phosphorus P

Platinum Pt

Potassium K

Rhodium Rh

Rubidium Kb

Ruthenium Ru

Samarium Sm

Scandium Sc

Selenium Se

Silicon Si

Silver Ag

Sodium .Na

Strontium Sr

Sulphur S

Tantalum Ta

Tellurium Te

Thallium Tl

Thorium Th

Tin Sn

Titanium Ti

Tungsten W

Uranium U

Vanadium Y

Ytterbium Yt

Yttrium Y

Zinc Zn

Zirconium Zr

What We Shall Study. — -In the course which you have
begun you will study only the most common elements and
their action upon one another. In this way you will be
able to learn much about the chemistry of many interesting
things, such as burning, the rusting of iron, the growth of
plants and animals, the extraction of useful metals from
their ores, the manufacture of illuminating-gas, of soap,
etc., etc., and at the same time you will acquire a know!
edge of the general principles of chemistry which will
enable you to take a more intelligent view of the universe
than you can without this knowledge.

16 TEE ELEMENTS OF CHEMISTRY

CHAPTEE II.
THE CHEMISTRY OF THE AIR.

The Air Causes Chemical Changes. — One of the most
interesting, most common, and most important chemical
changes with which we are familiar is that which is known
as burning. No matter how we may begin the study of
chemical facts, we are at once brought face to face with the
fact that the air takes part in chemical change.

Experiment 13. — In a small porcelain crucible arranged .as

shown in Fig. 3 put a small piece of lead. Heat by means of a

laboratory burner, and notice the changes which take place.

After the lead is melted stir with a thick iron

wire while heating. Continue to heat and stir

until the substance is no longer liquid. What

is its appearance now? Let it cool. Is it

lead ? What difference is there between the

action in this case and in the case of melting

ice and cooling the water down again ? Which

is chemical action and which physical action ?

Fig. 3. Why ?

Experiment 14. — Heat a piece of zinc in the same way as you

have just heated lead. What changes take place ?

Experiment 15. — Heat a piece of tin in the same way. What
changes take place ?

What Caused the Changes ? — By heating lead, zinc, and
tin in the air, then, they are changed to powders which do
not melt. The question will suggest itself, does the heat
alone cause these changes or has the air something to do
with them ? The air alone plainly does not cause the
changes, for they do not take place until the substances are

THE CHEMISTRY OF THE AIR. 17

heated. To learn whether the air has anything to do with
them we shall have to heat the substances in such a way as
to keep the air from getting at them. This can be done
by putting in the vessel something which melts and which
will float on the melted metal. Such a substance is ordi-
nary borax.

Experiment 16. — Kepeat Experiments 13, 14, and 15, adding in
each case enough borax to form a complete cover to the metal
after both are melted. Do the metals melt ? Are they changed
to powders as in the previous experiments ?

Many Similar Facts are Known. — The examples given
above are only a few of a large number of similar ones
mown. Hence the statement that many metals when
heated in the air undergo chemical change and are con-
verted into powders which do not melt. The powders are
formed by the action of the air on the heated metals, for
if the air be kept away from the metals the changes do not
take place.

The Metals Increase in Weight when Heated in the Air.
—If you were to weigh the metals used in Experiments 13,
14, and 15 and then weigh the powders obtained, you would
find that in each case the powder weighs more than the
metal. This fact taken together with the others already
learned shows that there is something in the air which at
high temperatures combines with the metals tin, zinc, and
lead.

Burning in the Air. — The phenomenon of burning takes
place in the air, and the question suggests itself, has the
air anything to do with the burning ? You know that if
you shut up a stove completely the fire dies down, and
unless the draught-door is opened the fire goes out. If you
want the fire to burn more actively you open the draught-
2

18 THE ELEMENTS OF CHEMISTRY.

doors when air is drawn in and the burning is made to
take place more rapidly. A fire burns better when air is
blown into it with a bellows. A candle is put out when
anything is brought down upon the flame in such a way as
to keep out the air. When a smouldering fire is covered
with ashes it goes out. All these facts, which are well
known to every one, make it appear probable that the aii
has something to do with burning, but they do not show
what. In order to learn this we shall have to experiment
carefully, noticing everything that takes place.

Experiment 17. — Fix a short bit of candle on a large flat cork

or a block of wood. Light the candle and place it with the block

on the surface of water contained in a pail or some other appro*

priate vessel. Place over it a good- sized glass vessel, either a

wide-mouthed bottle or a good-sized fruit- jar, as represented in

Fig. 4, so that the candle and cork are in the glass vessel and the

r\ mouth of the vessel is beneath the

^^"^^1^ surface of the water. Hold it in this

mi i'llh'^l ■ IB position for a few minutes and ob-

■1 'l^c^illNB serve what takes place. Does the

^Hl"'i"r jjfflK-'-^^g JiBli I ;,{fe'^ candle continue to burn ? Is all the

^fflT||fl ijjjI^SFj^flHl^^ a^r contained in the vessel used up

* -:-| |1 p|3& when the candle goes out ? Try the

Slllfii experiment a second time, and when

\^ "'li^^m^^^^^^^" the candle is nearly out raise the

Fig. 4. glass vessel so that air can get in.

Does this make any difference ? What difference ? What do

these experiments prove ?

A Candle Will Not Burn in the Air that is Left.— If,

after the candle has gone out, you place your hand or a
ground-glass plate over the mouth of the vessel and turn
it mouth upward, and then insert into it a lighted candle
on a wire, the candle will be extinguished. You see that
the air which is left in the vessel after a candle has binned
in it and gone out is not the same as ordinary air.

THE CHEMISTRY OF THE AIB.

19

Experiment 18. — Try the experiment just mentioned. The
candle on the wire should be arranged as shown in Fig. 5.

Does the Candle Increase in Weight ? —
You know that in burning the candle
gradually disappears, and from this you
would be inclined to think that it is de-
stroyed. But if you were to collect the
smoke which is given off and weigh it, you
would find that it weighs more than that
part of the candle which has burned up.
So that instead of there being a loss of
matter there is apparently a gain.

Fig. 5.

Experiment 19. — On one pan of an appropriate balance place
a candle, and directly over it suspend a wide glass tube contain-
ing pieces of caustic soda, a substance which has the power to
absorb most of the smoke given off from the burning candle.
Place a similar glass tube with caustic soda on the other pan of
the balance and exactly balance the two pans. Now light the
candle, and in the course of a few minutes the pan with the
candle on it will sink, showing that it is heavier than the other.

One Fifth of the Air is Used
up when Anything Burns in
a Closed Vessel.— By careful
experiments which it would
be difficult to repeat here it
has been shown that only one
fifth of the air is capable of
keeping up the process of
burning, while the rest is an
inactive substance in which
burning cannot take place.
If , for example, you could heat a piece of lead or zinc in
a closed vessel for a time, then let it cool and open the

Fig. 6.

20 THE ELEMENTS OF CHEMISTRY.

vessel under water, you would find that water would rush in
and fill about one fifth of the vessel, showing that this
much air had been used up. If you should weigh the metal
before and after heating you would find that it had in-
creased in weight, and if you should weigh the air used up
you would find that its weight is exactly equal to the in^
crease of weight of the metal. A great many experiments
of this kind have been performed, and they have shown
that when a substance burns it uses up something from the
air and increases in iveight exactly as much as the air loses.
The Air Consists Mainly of Two Substances. — The air
then consists of two substances, only one of which can keep
up the process of burning. This one is known as oxygen.
The other, in which things cannot burn, is known as nitro-
gen. Besides these the air always contains smaller quanti-
ties of other substances, particularly water vapor, carbonic
acid (or carbon dioxide), and ammonia. We shall soon
study these substances and see of what value they are in
the air. Oxygen and nitrogen are called elements because
no one has been able to decompose them and get anything
simpler from them.

OXYGEN. 21

CHAPTER III.
OXYGEN.

Occurrence of Oxygen. — Oxygen is the most widely dis-
tributed element, and it occurs also in very large quantity.
It has been stated that it forms between forty and fifty
per cent of the solid crust of the earth, eight ninths of
water and one fifth of the air by bulk.

Preparation of Oxygen. — We have oxygen around us in
great abundance, but it is mixed with nitrogen, and it is
difficult to separate the two so as to get the oxygen. The
easiest way to get oxygen is by heating something which
contains it. One of the simplest examples of this kind is
the oxide of mercury, which when heated gives mercury and
oxygen. When mercury itself is heated in the air for some
time to very near its boiling point it is gradually changed
to a red powder, just as lead and tin and zinc are changed
to powders when heated in the air. This powder is a com-
pound of mercury and oxygen. When the compound is
heated to a high temperature it is decomposed into its
elements, mercury and oxygen.

Collection of Oxygen. — The oxygen given off from the
oxide of mercury is most conveniently collected by causing
it to displace water. For this purpose the apparatus
should be arranged as represented in Fig. 7. On now
heating the oxide, the oxygen which is set free necessarily

22

THE ELEMENTS OF CHEMISTBY.

passes through the narrow tube and escapes beneath the
mouth of the inverted glass vessel which is filled with
water. The gas being lighter than water rises and the
water is displaced. The oxide of mercury should be heated
in a tube made of hard glass closed at one end.

Oxygen Made from Potassium Chlorate. — Another sub
stance which readily gives up oxygen when heated is po-
tassium chlorate or, as it is commonly called, chlorate of
potash. This is manufactured in large quantities and is
easily obtained. It contains the three elements potas-

Fig. 7.

slum, chlorine, and oxygen. When heated it gives up the
oxygen, and a compound of potassium and chlorine, knowi
as potassium chloride, very much like common salt, it
left behind.

Experiment 20. — Arrange an apparatus as shown in Fig. 8.
A represents a flask of 100 c.cm. capacity. By means of a good-
fitting rubber stopper one end of the bent glass tube B is con-
nected with it, and the other end, which should turn upward
slightly, is placed under the surface of the water in C. In A put
4 to 5 grams (about an eighth of an ounce) potassium chlorate,
and gently heat by means of a lamp. When gas comes off freely

OXYGEN.

23

bring the inverted cylinder B filled with water over the end of
the tube, and let the bubbles of gas rise in the cylinder. Exam-
ine the gas by placing a glass plate over the mouth of the vessel
containing it and inverting it. Insert into it a stick with a spark
on its end. What takes place ? Is the gas contained in the ves-
sel ordinary air ?

Fig. 8.

Oxygen Made by Heating a Mixture of Potassium Chlo^
rate and Manganese Dioxide. — The most convenient way to
make oxygen in the laboratory is to heat a mixture of
equal parts of potassium chlorate and manganese dioxide
or " black oxide of manganese." This mixture gives off
oxygen very readily when heated. The potassium chlorate
alone is decomposed under these circumstances,, the man-
ganese dioxide remaining unchanged. It is not known
how the manganese dioxide helps the action.

Experiment 21. — Mix 25 to 30 grams (or about an ounce) of
potassium chlorate with an equal weight of coarsely powdered

24

THE ELEMENTS OF CHEMISTRY*

manganese dioxide in a mortar0 Heat the mixture* in a glass
retort arranged as shown in Fig. 9, and collect the gas by

displacement of water in ap
propriate vessels — cylinders, bell
glasses, bottles with wide mouths,
etc.

Physical Properties of Oxy-
gen.— Having thus learned how
to get oxygen, you may proceed
to study its properties. In the
first place, the gas is invisible.
The slight cloud which ap-
pears in the vessels when the
gas is first collected is due
to the presence of a very
small quantity of a substance
which is not oxygen. If the vessels are allowed to stand
for a few minutes the cloud will disappear, and the vessels
will look the same as if they were filled with air0 The
gas is tasteless and inodorous. [Inhale a little from one of
the small bottles.] It is slightly heavier than the air.
When subjected to an extremely high pressure and low
temperature it becomes liquid. The properties of oxygen
to which reference has thus far been made are its physical
properties. These are its appearance, taste, smell, relative
weight, and changes in its condition, which still leave it
in the elementary form or uncombined chemically.

FiGo 9.

* Black oxide of manganese is sometimes adulterated with other
substances, and wiaen heated with potassium chlorate it may then
give rise to explosions. It should he tested before using by mixing
a little with potassium chlorate and heating in a test tube. If the de-
composition takes place quietly the substance may be used for the
preparation of oxygen.

OXYGEK 25

Chemical Conduct of Oxygen. — In order to get an idea
of the way in which oxygen acts upon some simple sub-
stances under ordinary circumstances a few experiments
should be performed. We want to learn: What changes
oxygen can effect in other substances; what conditions
are necessary in order that it may act chemically; what
products are formed, etc., etc.

The Action of Oxygen at the Ordinary Temperature.

Experiment 22. — Turn three of the bottles containing oxygen
with the mouth upward, leaving them covered with glass plates.
Into one introduce a little sulphur in a so-called deflagrating-
spoon, which is a small cup of iron or brass attached to a stout
wire which passes through a round metal plate, usually of tin
(see Fig. 10). In another put a little charcoal (carbon), and in a
third a piece of phosphorus * about the size of a pea. Let them
stand quietly and notice what changes, if any, take place.

What these Experiments Show. — These experiments show
that oxygen does not act upon sulphur and carbon when
brought in contact with them, and that the action upon
phosphorus is slight. We might perform experiments of
this kind with a great many substances,, and we should
reach the conclusion that at the ordinary temperature oxy-
gen does not readily act upon substances. Indeed, as the
air contains a considerable proportion of oxygen, it is clear
that oxygen does not readily act upon substances at ordi-
nary temperatures or action would constantly be taking place

* Phosphorus should be handled with great care. It is always
kept under water, usually in the form of sticks. If a small piece is
wanted, take out a stick ™ith a pair of forceps, and put it under water
in an evapora ting-dish. While it is under the water cut off a piece of
the size wanted. Take this out by means of a pair of forceps, lay it
for a moment on a piece of filter-paper, which will absorb most of the
water; then quickly put it in a spoon.

26 THE ELEMENTS OF CHEMISTRY.

between the air and many of the substances exposed
to it
Slow Action of Oxygen at the Ordinary Temperature.—

Upon some substances oxygen does act even at ordinary tem-
perature. Some metals, as iron, become covered with a
layer of rust when exposed to the air. This is due partly,
at least, to the action of the oxygen of the air. Wood and
other vegetable substances undergo slow decomposition
when exposed to the air, in consequence of the action of
the oxygen. Animal substances undergo decomposition
comparatively readily when exposed to the air. The pro-
cess of decay is partly due to the action of oxygen at the
ordinary temperature.

The Action of Oxygen in Animal Bodies. — The most im-
portant illustration of the action of oxygen at low tempera-
tures is that which takes place in our bodies and the bodies
of all animals. The food which we partake of undergoes
many changes; some of the substances uniting with oxygen.
Then , too, we take large quantities of oxygen into our lungs
inbreathing. This acts upon various substances which are
presented to it in the lungs; it combines with them, form-
ing other substances which can easily be got rid of. More
will be said in regard to the breathing of animals and plants
when the subject of carbon and its compounds with oxygen
is taken up.

The Action of Oxygen upon Heated Substances. — Sup-
pose that before putting them in the oxygen we heat the
substances used in Experiment 22, what will then take place?

Experiment 23. — In a deflagrating-spoon set fire to a little sul-
phur and let it burn in the air. Notice whether it burns with
ease or with difficulty. Notice the odor of the fumes which are

OXYGEN. 27

given off. Now set fire to another small portion and introduce it

in a spoon into one of the vessels containing oxygen, as shown in

Fig. 10. Does the sulphur burn more

readily in the oxygen or in the air?

Notice the odor of the fumes given off.

Is it the same as that noticed when the

burning takes place in the air ?

Experiment 24. — Perform similar
experiments with charcoal.

Experiment 25. — Burn a small piece
of phosphorus in the air and in oxygen.
In the latter case the light emitted from
the burning phosphorus is so intense Fig. 10.

that it is painful to some eyes to look at it. After the burning is
over let the vessel stand. Does it become clear ?

What Took Place in these Experiments? — In the first
place, the substances were simply heated before they were
introduced into the oxygen. Nothing was added to them.
It is clear, therefore, that while oxygen does not act upon
these substances at the ordinary temperature, it does act
upon them at higher temperatures. But what does the ac-
tion consist in? We can determine this only by a careful
study of the substances before and after the action. We
must know not only what substances are brought together,
hit also icliat the weight of each is; and we must know what
substances are left behind, and the exact iveight of these.
By means of accurate experiments it has been shown re-
peatedly that the substances which burn in oxygen disap-
pear as such, and that in each case a definite quantity of
oxygen is also used up. The result of the experiments can
be stated thus: The iveight of the substance hirned plus
the iveight of the oxygen used up is exactly equal to the
weight of the product formed.

28 THE ELEMENTS OF CHEMISTRY.

Burning is Combining with Oxygen. — From what we
have learned we may conclude that when a substance hums
in oxygen the act consists in the chemical combination of
the two.

Burning in the Air. — To determine whether burning in
the air is the same act as burning in oxygen it is neces-
sary to burn the same things in air and in pure oxygen
and see whether the products are the same. This has
been done a great many times, and always with the same
result. Whether a substance burns in the air or in pure
oxygen the same product is formed., and nothing else.
It is therefore certain that the act of burning in the air is
due to the presence of oxygen. As we have already seen^
there is another substance present in the air in large quan-
tity, and it is due to this fact that burning does not take
place as readily in the air as in oxygen.

Combustion. — By the term combustion in its broadest
sense is meant any chemical act which is accompanied
by an evolution of light and heat. Ordinarily, however,
it means the union of substances with oxygen as this
union takes place in the air, with evolution of light and
heat. Substances which have the power to unite with oxy-
gen are said to be combustible, and substances which have
not this power are said to be incombustible. Most of the
elements combine with oxygen under proper conditions,
and are therefore combustible. Most compounds formed
by the union of oxygen with combustible substances are
incombustible. They contain oxygen and they cannot di-
rectly combine with any more.

Some Substances which do not Burn in the Air Burn
in Oxygen. — The best illustration of this fact is that of
iron. This metal, as you know, does not burn in the air. If

OXYGEN. 29

it did, all our stoves,, iron vessels, and iron buildings would
burn up. In pure oxygen, however, iron burns readily.

Experiment 26. — Straighten a steel watch-spring * and fasten
it in a piece of metal, such as is used for fixing a defiagrating-
spoon in an upright position; wind a little thread around the
lower end, and dip it in melted sulphur. Set fire to this and
insert it into a vessel containing oxygen. For a moment the sul-
phur will burn as in Experiment 23; but soon the steel will begin
to burn brilliantly, and the burning will continue as long as there
is oxygen left in the vessel. The phenomenon is of great beauty,
especially if observed in a dark room. The walls of the vessel be-
come covered with a dark reddish-brown substance, some of
which will also be found at the bottom in large pieces.

Kindling Temperature. — You have seen that substances
do not usually combine with oxygen at ordinary tempera-
tures, but that in order to effect the union the temperature
must be raised. If this were not the case it is plain that
every combustible substance in nature would burn up, for
the air supplies a sufficient quantity of oxygen for this
purpose. Some substances need to be heated to a high
temperature before they will combine with oxygen ; others
require to be heated only slightly. Every combustible sub-
stance has its kindling temperature ; that is, the tempera-
ture at which it will unite with oxygen. Below this tem-
perature it will not unite with oxygen. Watch a stick of
wood burning, and watch how, as we say, ^the fire creeps"
along it. The reason of the slow advance is simply this :
only those parts of the stick which are nearest the burning
part become heated to the kindling temperature. They

* Old watch-springs can generally be had of any watch maker or
mender for the asking. They can be straightened by pulling them
between the thumb and some hard substance, such as a glass rod or
a round pencil.

30 THE ELEMENTS OF CHEMISTRY.

take fire and heat the parts nearest them, and so on grad-
ually throughout the length of the stick.

Heat a Result of Combustion. — We know that whenever
a thing burns it gives out heat, and generally light. The
heat is a result of the act of chemical combination, and the
light is due to the heat. Whenever chemical combination
takes place heat is given off. It is caused by the rapid
coming together of the particles of the substances which
combine, just as a bullet is heated by being rapidly pro-
jected against a hard target which stops it„

Chemical Energy and Chemical Work. — Any substance
which has the power to combine with others can do chem-
ical loorlc; it possesses chemical energy. Thus all combus-
tible substances can do work. In combining with oxygen
heat is given off, and this can be changed into motion. To
go back to the example of the steam-engine, which was re-
ferred to in Chapter I., the cause of the motion is the burn-
ing of the fuel.

Products of Combustion. — The substances formed in com-
bustion are in general known as oxides. The compound
of zinc and oxygen is called zinc oxide; that of silver and
oxygen, silver oxide, etc.

COMBINING WEIGHTS. 31

CHAPTER IV.
COMBUSTING WEIGHTS.

Elements Combine in Definite Weights. — A certain weight
of tin always combines with a definite weight of oxygen.
If equal weights of sulphur and iron be mixed and caused to
act chemically by the aid of heat, it will be found that some
of the sulphur is left over in the uncombined state after the
action is over. If we should take twice as much iron as
sulphur, then, after the action, some iron would be left
over. An extensive examination has shown conclusively
that each chemical compound always contains the same ele-
ments in exactly the same proportions. The compound of
sulphur and iron always contains exactly 36.36 per cent of
sulphur and 63.64 per cent of iron. The compound of tin
and cxygen always contains exactly 78. 67 per cent of tin
and 21.33 per cent of oxygen, and so on throughout the list
%of chemical elements.

The Law of Definite Proportions. — These facts were dis-
covered by the united efforts of a large number of chemists
continued through several years.' They are of great impor-
tance. They are summed up in the general statement:

Chemical combination always takes place between definite
masses of substances.

This is known as the law of definite proportions*

What a Natural Law is. — It is simply a statement of what
we have every reason to believe to be the truth. Every

32

THE ELEMENTS OF CHlJMXSTBZ

fact known to us in regard to chemical combination is in
accordance with the law of definite proportions. It ex-
presses what has been learned by a study of chemical facts.
This law,, as well as other natural laws, can never be proved
to be absolutely true, for the reason that we cannot examine
every case to which the law applies. But if, after examin-
ing a very large number of cases, we find that the law holds
true in them, we may conclude that it is true of all cases.
When we say that all bodies attract one another, do w&
know this to be absolutely true? Certainly not. But we
do know that so far as those bodies are concerned which
come under our observation the statement is true, and
therefore we have reason to believe that it is true of all
bodies.

Proportions by Weight in which the Elements Combine. —
A careful study of the figures representing the composi-
tion of chemical compounds reveals a remarkable fact re-
garding the relative quantities of one and the same element
which enter into combination with other elements. The
proportions by weight in which some of the elements com-
bine chemically are stated in the following table :

Sulphur 1 ;
Oxygen 1.

Iron 7 ;
Oxygen 2.

Iron 7 ;
Sulphur 4.

Magnesium 3 ;
Oxygen 2.

Tin 59 ;
Oxygen 16.

Zinc 65 ;
Oxygen 16.

Tin 59 :
Sulphur 16.

Zinc 65 ;
Sulphur 32,

Sodium 23 ;
Oxygen 8.

Sodium 23 ;
Sulphur 16.

Potassium 39 ;
Oxygen 8.

Potassium 39 ;
Sulphur 16.

You see that for iron, tin, zinc, sodium, and potassium the
same figures are used, whether you have the compounds of
these elements with oxygen or with sulphur, Now, if we

COMBINING WEIGHTS. S3

were to determine the composition of all compounds which
contain zinc, we should find that the relative quantity of
zinc present could, in nearly all cases, be expressed by the
figure. 65. Similarly the quantity of sodium in sodium
compounds could be expressed by the figure 23, and that of
potassium in potassium compounds by 39.

Combining Weights of the Elements. — For every element
a certain number can be selected, such that the proportions
by weight in which this element enters into combination
with others can be expressed by the number or by a simple
multiple of it. These numbers are called the combining
iveiglits. It is not by any means an easy matter to deter-
mine w^hich numbers are most convenient for all cases; and
if the selection is to be determined solely by convenience,
there may be differences of opinion as to what is most con-
venient. We shall see a little later that while the numbers
primarily express the combining weights and nothing else,
and are based solely upon determinations of the composition
of chemical compounds, they have come to have a deeper
meaning, and are now determined by methods which you
cannot well understand until you have gone further into
chemistry. The facts which it is of the highest impor-
tance that you should understand now are :

(1) That chemical action takes place between definite
weights of substances ; and

(2) That the relative weights of the elements which enter
into combination with one another can be expressed by
numbers called the combining weights.

Symbols of Chemical Compounds. — You have learned that
the chemist uses a kind of short-hand to express the names
of the elements. Instead of the name oxygen he writes
the symbol 0, etc. Now these symbols stand not only fox

34 THE ELEMENTS OF CHEMlSTBY.

the names but also for the combining weights of the ele-
ments. Thus, 0 stands not only for the name oxygen but
for 16 parts by weight; Fe stands for 56 parts by weight
of iron, etc. To express a compound in the short-hand,
the symbols of the elements contained in it are simply
placed side by side. Thus, common salt or sodium chloride
consists of the elements sodium and chlorine, which are
combined in the proportion of their combining weights.
The symbol of the compound is NaOl, which means a com-
pound of the elements sodium and chlorine in the propor-
tion 23 of sodium and 35.5 of chlorine.

How Chemists Express Chemical Reactions.— The symbols
are of great convenience when it is desired to express what
has taken place in a chemical reaction. Thus you have
seen that when the compound mercury oxide, HgO, is
heated, it is decomposed into mercury and oxygen, a fact
which is clearly expressed by the equation

HgO-Hg + O,

which tells not only the fact that decomposition takes place
but the proportions by weight in which the substances take
part. Thus, the compound, HgO, contains the elements in
the proportion of 200 parts of mercury to 16 parts of
oxygen. When 216 parts of this compound are decom-
posed 200 parts of mercury and 16 parts of oxygen are
obtained.

A Chemical Problem. — Suppose you wished to know how
much oxygen is contained in 50 grams of mercury oxide,
how could you determine it? You know that in 216 parts
of the compound there are 16 parts of oxygen; or, that in
216 grams of the compound there are 16 grams of oxygen.
How many grams of oxygen are there in 50 grams of the

COMBINING WEIGHTS. 35

compound? Plainly the answer is given by solving the
expression

216 : 50 :: 16 : the number of grams of oxygen contained
in 50 grams of the oxide.

Law of Multiple Proportions. — Two elements frequently
combine in more than one set of proportions. Thus, while
ordinarily iron and sulphur combine in the proportion 56
of iron to 32 of sulphur, they also combine in the propor-
tion 56 of iron to 64 of sulphur. Tin combines with oxy-
gen in two proportions, forming two distinct compounds.
In one 118 parts of tin are combined with 16 parts of oxy-
gen; in the other 118 parts of tin are combined with 32
parts of oxygen. The elements potassium, chlorine, and
oxygen combine in several proportions as represented here :

Potassium 39 39 39 39

Chlorine 35.5 35.5 35.5 35.5

Oxygen 16 32 48 64

It will be observed that while in the compounds men-
tioned the quantities of oxygen and sulphur united with
the same element or elements vary, these quantities are
closely related to one another. In the case of iron and sul-
phur there is twice as much sulphur, relatively, in one
compound as in the other. So, also, in the compounds of
tin and oxygen there is twice as much oxygen combined
with a given quantity of tin in one case as in the other.
Finally, in the four compounds which are made up of
potassium, chlorine, and oxygen the quantity of oxygen
varies, being twice as great in the second compound as in
the first, three times as great in the third, and four times
as great in the fourth. These facts, and others of the
same kind, are summed up in the Law of Multiple Propor-
tions, which may be stated thu&:

36 THE ELEMENTS OF CHEMISTRY.

If two elements, A and B, combine in different propor-
tions, the relative quantities of B which combine with any
fixed quantity of A bear a simple ratio to one another.

Symbols of Compounds of Elements Combined in More than
One Proportion. — As has already been stated, when two
elements combine in the simplest proportion the symbol
of the compound is made by putting the symbols of the
elements side by side, as in HgO, NaCI, etc., etc. If it i
desired to represent compounds of the same elements com-
bined in different proportions, use is made of small figures
placed below the line, as in the symbols S02, C02, H2S04,
etc., etc. The meaning of the figures is simply this : In
the compound S02 sulphur and oxygen are combined in the
proportion of the combining weight (32) of sulphur and
twice the combining weight (16) of oxygen, or 32 parts of
sulphur to 32 parts of oxygen, which happens to be the
same as 1 part of one to 1 part of the other. The symbol
H2S04 represents a compound made up of hydrogen, sul-
phur, and oxygen in the proportion ttvice the combining
weight of hydrogen (1), the combining weight of sulphur
(32) and. four times the combining weight (16) of oxygen ;
or 2 parts hydrogen, 32 parts sulphur, and 64 parts oxygen,
making all together 98 parts of the compound.

Problem. — How much sulphur is there in 60 grams of the com-
pound H2SO4 (sulphuric acid) ? How much oxygen ? How much
hydrogen ?

ft f ,£,/

*/<r -

ft, WYYYJV

NITROGEN. 37

CHAPTER V.
NITROGEN.

Occurrence of Nitrogen.— You have already learned that
about four fifths of the bulk of the air is nitrogen. This
element is also found in combination in a large number of
substances in nature. It is found in the nitrates, as salt-
petre or potassium nitrate, KN03, and Chili saltpetre or
sodium nitrate, JSTaN03. It is also found in the form of
ammonia, which is a compound of nitrogen and hydrogen
of the formula NH3. Ammonia occurs in small quantity
in the air, and is formed under a variety of conditions,
which will be referred to when the substance is considered.
Nitrogen occurs, further, in most animal substances in
chemical combination.

Preparation of Nitrogen. — The most convenient way to
prepare nitrogen is to burn a piece of phosphorus in a bell-
jar over water. The reasons why phosphorus is better for
the purpose than most other substances are (1) because it
burns, that is combines with oxygen, easily ; and (2) be-
cause the compound which it forms with oxygen (the pro-
duct of combustion) is a solid and dissolves in water. If
the product of combustion were a gas this would remain
mixed with the nitrogen after the combustion.

Experiment 27. — Place a wide-mouthed jar over water in a
larger vessel of water. In the middle of a fiat cork about three
inches in diameter fasten a small porcelain crucible, and float
this on the water in the trough. Put in it a piece of phosphorus

38 THE ELEMENTS OF CHEMISEBY.

about twice the size of a pea, and set fire to the phosphorus.
Quickly place the jar over it on a support which will prevent the
jar from sinking more than an inch or two in the water. At first
some air will be driven out of the vessel on account of the expan-
sion due to the heat. After the burning has stopped cover the
mouth of the jar with a glass plate and turn it mouth upward.
Try the effect of introducing successively several burning bodies
into the nitrogen, as, for example, a candle, a piece of sulphur,
phosphorus, etc.

Other Substances besides Phosphorus maybe Used. —Any-
thing that has the power to combine with oxygen may be
used in the preparation of nitrogen from the air. Metallic
copper is convenient, and is not unfrequently used. It is
only necessary to pass air over heated copper, when the
metal combines with oxygen, forming the solid copper ox-
ide, CuO, leaving the nitrogen uncombined.

Properties of Nitrogen. — You have seen that nitrogen is
a colorless, tasteless, inodorous gas. It does not support
combustion, nor does it burn. [Suppose nitrogen were
combustible, what would be the composition of the atmos-
phere ?] Nitrogen not only does not combine with oxygen
readily, but it does not combine with any other element,
easily except at a very high temperature, and then with only
a few. Just as it does not support combustion, so also it
does not support breathing. An animal would die in it,
not on account of any active poisonous properties possessed
by it, but for lack of oxygen. In the air it serves the use-
ful purpose of diluting the oxygen. If the air consisted
only of oxygen, all processes of combustion would certainly
be much more active than they now are. What the effect
on animals of the continued breathing of oxygen would be
it is difficult to say, as but few experiments on this subject
h&ve been made.

NITBOGEN. 39

Nitrogen and Oxygen are Mixed together, not Chemi-
cally Combined in the Air. — It is not an easy matter to
prove this statement satisfactorily, but the evidence is so
strong that no chemist doubts it.

(1) If nitrogen and oxygen are mixed together, the
mixture acts just like air. When they are mixed there is
nothing to show that chemical action takes place. You
have seen that the combination of two substances gives rise
to heat. When nitrogen and oxygen are mixed together
there is no change in the temperature of the gases.

(2) Substances known to be chemical compounds do not
vary in composition; that of the air does vary slightly.

(3) Air dissolves somewhat in water. If air which has
been thus dissolved be pumped out and analyzed, it is
found to have a composition different from that of ordinary
air. Instead of containing 1 volume of oxygen to 4 vol-
umes of nitrogen, it will contain 1 volume of oxygen to
1.87 volumes of nitrogen. The relative quantity of oxygen
is much larger in air which has been dissolved in water
than in ordinary air. This is due to the fact that oxygen
dissolves more readily in water than nitrogen does. If the
gases were in chemical combination the compound would
probably dissolve without changi of composition.

Summary.- — The air consists of nitrogen and oxygen in
the proportion of 4 volumes of the former to 1 volume of the
latter. Oxygen supports combustion; nitrogen does not0
Oxygen supports respiration; nitrogen does not. Oxygen
and nitrogen are elements. They are not chemically com-
bined in the air. Oxygen is made by heating substances
which contain it, as, for example, mercury oxide and po-
tassium chlorate. Nitrogen is made by burning phos-
phorus in a closed vessel containing air.

40 THE ELEMENTS OF CHEMISTBY.

Elements combine in definite proportions by weight
(law of definite proportions).

In each element a number may be selected by means of
which the proportion by weight in which it enters into
combination may be expressed (combining weights) 6

If an element combines with another in more than one
proportion, the quantities which enter into combination
with a fixed quantity of the second element bear a simple
ratio to one another (law of multiple proportions).

WATER. 41

CHAPTER VI

WATER.

Occurrence of Water in Nature. — The wide distribution

of water on the earth is familiar to every one. But water

also occurs in forms and conditions which prevent it from

being easily recognized. Thus, all living things contain a

large proportion of water, which can be driven off by heat.

If a piece of wood or a piece of meat be heated, water

passes off.

Experiment 28. — In a dry tube heat gently a small piece of
wood. What evidence do you obtain that water is given off ? Do
the same thing with a piece of fresh meat.

Large Proportion of Water in Animal and Vegetable
Substances. — The proportion of water in animal and vege-
table substances is very great. If the body of a man
weighing 150 pounds were put into an oven and thorough-
ly dried there would be left only about 50 pounds of solid
matter, all the rest being water. As all meat, vegetables,
and food-stuffs in general contain a similar large propor-
tion of water, it is evident that water is an important arti-
cle of commerce. When you buy four pounds of beef you
pay for about three pounds of water and one pound of
solid matter.

Water of Crystallization. — Many chemical compounds
when deposited from solutions in water often appear in
regular forms called crystals. These frequently enclose
w#ter in chemical combination, and this water is necessary

42 THE ELEMENTS OF CHEMISTRY.

in order that the substance may exist in the form of crys-
tals. Water thus held in combination is called water of
crystallization.

Experiment 29. — Dissolve some ordinary alum in water (6-8
ounces alum to 200 c.cm. water) by the aid of heat Filter
through a plaited filter and allow the filtered solution to cool.
Crystals of alum will be deposited. Pour off the liquid above
and place a few of the crystals on a piece of dry filter-paper.
After the water is all absorbed from them and they appear dry,
put them in a dry test-tube and heat gently. What evidence
have you that water is contained in the crystals ?

Experiment 30.— Perform a similar experiment with some
gypsum, which is the natural substance from which ' ' plaster of
Paris' ' is made.

Experiment 31. — Heat a few small crystals of copper sulphate
or " blue vitriol." In this case the loss of water is accompanied
by a loss of color. After all the water is driven off, the powder
left behind is white. On dissolving it in water, however, the so-
lution will be seen to be blue ; and if this solution be evaporated
until the substance is deposited, it will appear in the form of blue
crystals.

Efflorescent and Deliquescent Substances. — Some sub-
stances which contain water of crystallization give it up
very easily when exposed to the air. Such substances are
called efflorescent.

Experiment 32. — Select a few crystals of sodium sulphate or
Glauber's salt which have not lost their lustre. Put them on a
watch-glass, and let them lie exposed to the air for an hour or
two. They soon lose their lustre, and become white and powdery
on the surface.

Some compounds if deprived of their water of crystalli-
zation will take it up again when allowed to lie in an
atmosphere containing moisture. Such substances are
called deliquescent. As the air always contains moisture,
it is only necessary to expose such compounds to the air
in order to notice the change. It is well shown by the

WATER. 43

compound calcium chloride, Ca012. This substance has a

remarkable power of attracting water and holding it in

combination.

Experiment 33. — Expose a few pieces of calcium chloride to
the air. Its surface will soon give evidence of being moist, and
after a time the substance will dissolve in the water which is ab-
sorbed.

Water is a Compound. — That water is a compound and

not an element can be shown by passing an electric current

through it. If the ends of the wires connected with a

galvanic battery be put in water a short distance apart it

will be noticed that bubbles of gas rise from each wire.

As these gases cannot well come from the wires, the most

probable supposition is that they are formed from the

water.

Experiment 34. — To the ends of the copper wires connected
with two cells of a Bunsen's or Grove's battery fasten small plati-
num plates,, say 25 mm. (1 inch) long by 12 mm. (■§■ inch) wide.
Insert these platinum ends into water contained in a shallow
glass vessel about 15 cm. (6 inches) wide and 7 to 8 cm. (3 inches)
deep, taking care to keep them separated from each other. ISTo
action will take place, for the reason that water will not conduct
the current, and hence when the platinum ends are kept apart
there is no current. By adding to the water one tenth its own
volume of strong sulphuric acid it acquires the power to conduct
the current. It will then be observed that bubbles rise from each
of the platinum plates. In order to collect the gases the ap-
paratus may be arranged as shown in Fig. 11. A and B repre-
sent glass tubes which may conveniently be about 30 cm. (1
foot) long and 25 mm. (1 inch) internal diameter. They should be
marked by means of a file, or by etching, so that equal divisions
can be recognized. Tubes thus marked so that the divisions in-
dicate cubic centimetres are most convenient, and are easily ob-
tained of dealers in chemical apparatus. The tubes are first
filled with the water containing one tenth its volume of sulphuric
acid, and then placed with the mouth under water in the vessel
C. The platinum plates are now brought beneath the inverted

44

THE ELEMENTS OF CHEMISTRY.

tubes. The bubbles will rise in them and displace the water.
Gradually the water will be completely forced out of one of the
tubes, while the other is still half full of water. The substance
which we have thus collected in each of the tubes is an invisible
gas. After the first tube is full of gas, remove it by placing your
thumb over the mouth. Turn it mouth upward, and at once ap-
ply a lighted match to it. A flame will be noticed. The gas

Fig. 11.

burns. Is it air ? Is it oxygen ? Is it nitrogen ? In the mean
time the second tube will have become filled with gas. Eemove
the tube in the same way, and insert a thin piece of wood with a
spark on the end. Does this gas act like oxygen ? The gas col-
lected in the tube which first became filled is known as hydrogen,
while the other is oxygen.

What the Experiment Shows. — The experiment just
performed shows that when an electric current is passed
through water hydrogen and oxygen are obtained, and
also that there is obtained twice as much hydrogen by
bulk as oxygen. Whether these are the only elements con-
tained in water can only be shown by further experiments.
But it will be necessary first to learn something about hy-
drogen.

HYDB0GE2T. 45

\A

CHAPTER VII.

HYDROGEN.

Occurrence of Hydrogen. — Hydrogen is found in nature
very widely distributed, and in large quantity. It forms
one ninth the weight of water, and is contained in all the
principal substances which enter into the composition of
plants and animals.

Preparation of Hydrogen. — It may be obtained

(a) By decomposition of water by means of the electric
current;

(b) By decomposition of water by means of certain
metals;

(c) By the action of substances known as acids on metals.
The first method has already been illustrated in Experi-
ment 34.

Experiment 35. — Throw a small piece of sodium* on water.
While it is floating on the surface apply a lighted match to it.
What takes place ? The flame is due to burning hydrogen, the
flame beiug colored yellow by the presence of sodium, some of
which also burns.

Experiment 36. — Certain metals which do not decompose
water at ordinary temperatures, or which decompose it slowly,
decompose it easily at elevated temperatures. This is true of
iron. If steam be passed through a tube containing pieces of

* The metals sodium and potassium are kept under kerosene oil.
When a small piece is wanted, take out one of the larger pieces
from the bottle, roughly wipe off the oil with filter-paper, and cut off
a piece the size needed. It is not advisable to use a piece larger than
a pea.

46

THE ELEMENTS OF CHEMISTRY.

iron turnings or fine bright iron wire heated to redness, the
water is decomposed, the oxygen is retained by the iron in chem-
ical combination, while the hydrogen is liberated. In this ex-
periment a porcelain tube with an internal diameter of from 20
to 25 mm. (about an inch) and a gas-furnace are desirable,
though a hard glass tube and a charcoal-furnace will answer.
The arrangement of the apparatus is shown in Fig. 12.

Fig. 12.

Water-gas. — Many other substances have the power to
decompose water and set hydrogen free. The fact that a
combustible gas can be obtained from water has led to
many attempts to manufacture gas for heating and illu-
minating purposes from water. There is, however, no
cheap substance which has the power to decompose water
at ordinary temperatures. Heat must be used, and it is
generally the case that the quantity of heat required to
effect the decomposition is greater than that which would
be obtained by burning the hydrogen formed. The so-
called "water-gas" nowr so extensively manufactured in the
United States both for illuminating and heating is made
by the action of highly heated hard coal on steam. The
essential part of the chemical reaction is represented by
the equation

C + H20 = CO -f 2H,

HYDBOGEN-. 47

Carbon (or coal) acting upon the water (H20) combines
with the oxygen, forming the compound carbon monoxide,
CO, and leaving the hydrogen uncombined. Both pro-
ducts are gases, and both burn; and when this mixture is
enriched by some of the oils obtained from petroleum it
burns well and gives a good light.

The Common Acids. — Hydrogen is most conveniently
made in the laboratory by treating a metal with an acid.
As will be seen later, acids are substances which contain
hydrogen, and which give up this hydrogen very easily and
take up other elements in the place of it. Among the
common acids found in every laboratory are hydrochloric
acid, sulphuric acid, and nitric acid. These compounds
will be considered in due time.

Hydrogen is Generally Given off when a Metallic Ele-
ment Acts upon an Acid.— This is shown as follows:

Experiment 37. — In a cylinder or test-tube put some small
pieces of granidated zinc, and pour upon it enough ordinary
hydrochloric acid to cover it. What do you notice ? After the
action has continued for a minute or two apply a lighted match
to the mouth of the vessel. What takes place ? Try the same ex-
periment with sulphuric acid diluted with six times its volume of
water. * What is the result ? The gas given off is hydrogen.
For the purpose of collecting it the operation is best performed in
a bottle with two necks called a Wolff's flask (see Fig. 13), or in
a wide-mouthed bottle in which is fitted a cork with two holes
:(see Fig. 14). Through one of the holes passes a funnel-tube,
and through the other a glass tube bent in a convenient form.
Put a small handful of granulated zinc into the bottle and

* If it is desired to dilute ordinary concentrated sulphuric acid
with water, the acid should be poured slowly into the water while the
mixture is constantly stirred. If the water is poured into the acid,
the heat evolved at the places where the two come in contact may be
Bo great as to convert the water into steam and cause the strong acid
to spatter.

48

THE ELEMENTS OF CHEMISTRY.

pour upon it enough of a cooled mixture of sulphuric acid and
water (1 volume concentrated acid to 6 volumes of water) to cover
it. Usually a brisk evolution of gas will take place at once.
Wait two or three minutes, and then collect some of the gas

Fig 13.

Fig. 14.

by displacement of water. Should the action become slow add a
little more of the dilute acid. It will be well to fill several cylin-
ders and bottles with the gas.

Physical Properties of Hydrogen.— Hydrogen is a color-
less, inodorous, tasteless gas. Made by the action of zinc
on acids, it has a slightly disagreeable odor. This is due
to the presence of small quantities of impurities. If these
be removed the odor disappears.

Experiment 38.— Pass some of the gas through a solution of
potassium permanganate ; collect some of it, and notice whether
it has an odor. The apparatus should be arranged as shown in
Fig. 15. The solution of potassium permanganate is, of course,
contained in the small cylinder, A, and the tubes so arranged that
the gas bubbles through it.

The gas is not poisonous, and may therefore be inhaled

HYDBOGEW.

49

with impunity. We could not, however, live in an atmos-
phere of hydrogen, as we must have oxygen. It is the

Fig. 15.

lightest substance known, being fourteen and a half times
lighter than air and sixteen times lighter than oxygen.

Experiment 39. — Place a vessel containing hydrogen with the
mouth upward and uncovered. In a short time examine the gas
and see whether it is hydrogen.

Experiment 40. — Gradually bring a vessel containing hydro-
gen with its mouth upward be-
low an inverted vessel contain-
ing air, in the way shown in Fig.
16. The air will be displaced.
On examination, the inverted ves-
sel will be found to contain hydro-
gen, while the one with the mouth
upward will contain none. The
gas is thus poured upward. Fig. 16.

Experiment 41. — Soap-bubbles filled with hydrogen rise in the

50 THE ELEMENTS OF CHEMISTRY.

air. The experiment is best performed by connecting an ordi-
nary clay pipe by means of a piece of rubber tubing with the
exit-tube of a gasometer filled with hydrogen. Small balloons of
collodion are also made for showing the lightness of ^hydrogen
Large balloons are always filled with hydrogen or some other
light gas. Some kinds of illuminating-gas are rich in hydrogen
and may therefore be used for the purpose.

Weight of Hydrogen Compared with that of Oxygen.—

A litre of hydrogen at 0° 0. and under the pressure of the
atmosphere weighs 0. 089578 gram. A litre of oxygen under
the same conditions weighs 1.429 grams. These figures are
to each other as 1 to 16. But the figures 1 and 16 are the
combining weights of hydrogen and oxygen; that is to say>
they are the figures best adapted to expressing the relative
weights of these elements which enter into combination.
A similar connection exists between the relative weights of
equal volumes of some other elementary gases and their
combining weights, as will be seen later.

All Combining Weights are Referred to that of Hydro-
gen.— The figures called the combining weights express
the relations between the weights of the different elements
which enter into combination. When we say that the
combining weight of hydrogen is 1 and that of oxygen is
16, we mean that the weight of oxygen which generally
enters into combination is sixteen times as great as the
weight of hydrogen which enters into combination. The
figures 2 and 32 would express this relation just as well; so
would 6 J- and 100; but the simplest figures which can be
used are 1 for hydrogen and 16 for oxygen. Having
adopted these, all other combining weights are referred ±o
these.

Hydrogen a Liquid. — At a very low temperature and
high pressure hydrogen becomes liquid.

HYDBOGEHT. 51

Chemical Properties of Hydrogen. — Under ordinary cir-
cumstances hydrogen is not a particularly active element.
It does not unite with oxygen at ordinary temperatures,
but, like wood and most other combustible substances, needs
to be heated up to the kindling temperature before it will
burn. You have seen that it burns if a lighted match be
applied to it. The flame is colorless, or very slightly blue.
As burned under ordinary circumstances the flame is col-
ored, in consequence of the presence of foreign substances;
but that it is colorless when the gas is burned alone can be
shown by burning it from a platinum tube, which is itself
not acted upon by the heat.

Experiment 42. — If there is no small platinum tube available,

roll up a small piece of platinum -foil and melt it into the end of

a glass tube, as shown in Fig. 17. Connect the burner thus

made with a bottle or gasometer

containing hydrogen, and after ||

the gas has been allowed to issue mk

from it for a moment * set fire to 1 |B

it. In a short time it will be seen JW

that the flame is practically color- F™^ Jw

less and gives no light. That it ~~

Fig 17
; is hot is shown by holding a piece

! of platinum wire or a piece of some other metal in it.

The Burning of Hydrogen. — Hydrogen burns. You have

I already learned that burning consists in combining with

! oxygen. On the other hand, substances which burn in the

air are extinguished when put in a vessel containing hydro-

' gen. This is the same as saying that a body which is com-

* Always be cautious in working with hydrogen. The danger con-
sists in the fact that a mixture of hydrogen and oxygen or hydrogen
and air is extremely explosive. It requires a flame or spark to explode it.
Always let the gas escape for a time, and collect a test-tube full and
light to see if it will burn quietly, before applying a flame tp it.

52 THE ELEMENTS OF CHEMISTRY.

bining with oxygen does not continue to combine with
oxygen when it is put in an atmos<
phere of hydrogen, and does not com-
bine with hydrogen. This is ex-
pressed by saying that hydrogen does
not support combustion.

Experiment 43. — Hold a wide-mouthed
bottle or cylinder filled with hydrogen with
the mouth downward. Insert into the
vessel a lighted taper held on a bent wire,
as shown in Fig. 18. The gas takes fire
at the mouth of the vessel, but the taper
is extinguished. On withdrawing the 'ta-
per and holding the wick for a moment in
1 * the burning hydrogen, it will take fire,

but on putting it back in the hydrogen it will be again extin-
guished. Other burning substances should be tried in the same
way.

WATER.

53

CHAPTER VIII.

WATER {Continued).

Composition of Water. — In Chapter VI. you learned that
hydrogen and oxygen are both set free when an electric
current is passed through water. It remains to be seen
whether these are the only elements contained in water.
If water consists only of hydrogen and oxygen, then when
these elements combine water should be formed. But
when hydrogen burns it combines with oxygen. Is water
formed when hydrogen burns ?

Experiment 44. — Pass hydrogen from a generating-flask or a
gasometer through a tube containing some substance that will
absorb moisture, for all gases collected over water are charged
with moisture. You have seen in Experiment 33 that calcium

Fig. 19.

chloride has the power to absorb moisture. It is extensively used
in the laboratory for the purpose of drying gases, and it may be
used in the present experiment. It should be in small pieces

54 THE ELEMENTS OF CHEMISTBY.

about the size of a pea, not powdered. After passing the hydr<
gen through the calcium chloride, pass it through a tube ending
in a narrow opening and set fire to it. (Take the precaution
mentioned in the foot-note, page 51.) If now a dry vessel be held
over the flame, drops of water will condense on its surface and
run down. A convenient arrangement of the apparatus is shown
in Fig. 19. A is the calcium chloride tube. Before lighting the
jet hold a glass plate in the escaping gas, and see whether water is
deposited on it. Light the jet before putting it under the bell- jar;
otherwise, if hydrogen is allowed to escape into the vessel it will
contain a mixture of air and hydrogen, and this mixture is explo-
sive.

Hydrogen and Oxygen do not Combine at the Ordinary
Temperature. — If they did,, hydrogen would take fire the
moment it comes in contact with the air. If we mix the
gases together and allow the mixture to stand unmolested,
it remains unchanged. If, however, we should bring a
spark or a flame in contact with the mixture a violent ex-
plosion would occur, and a careful examination would show
that the explosion is caused by the combination of the two
gases. The combination causes heat. The heat causes
the gases to expand greatly and suddenly, and the noise is
caused by this sudden expansion. The expansion is fol-
lowed by a contraction.

Experiment 45.- — Mix hydrogen and oxygen in the proportion
of about 2 volumes of hydrogen to 1 volume of oxygen in a gas-
ometer or large bottle. Fill soap-bubbles, made as directed in Ex
periment 41, with this mixture and allow them to rise in the air.
As each one rises bring a lighted taper in contact with it, when
a sharp explosion will occur. Great care must be taken to keep
all flames away from the vicinity of the vessel containing the mix-
ture.

Measuring the Volumes of Hydrogen and Oxygen which
Combine to Form Water. — The last experiment simply
showed that when a flame comes in contact with a mixture

WATER. 55

of hydrogen and oxygon an explosion occurs. To show
what else takes place the experiment mast be performed in
a closed vessel. This experiment has been performed many
times. As it would be difficult for you to repeat it you
will have to be satisfied with a description of the apparatus
used and a statement of the result obtained. A tube is
used which is marked on the outside so that the volume of
gases contained in it can be seen, and has two small plati-
num wires passed through it at the closed end, c^
nearly meeting inside and ending in loops out-
side, as shown in Fig. 20. It is called a eudio-
meter. It is filled with mercury and inverted in a
trough containing mercury. A quantity of pure
hydrogen is now passed up into the tube and its
volume accurately measured. Then just half this
volume of oxygen is introduced, and after the mix-
ture has stood for a few minutes, so that the gases
can become thoroughly mixed, an electric spark is
passed between the wires inside the tube by con-
necting the loops with the poles of a small Euhm-
korff coil or with a Leyden jar. The explosion
takes place noiselessly and with very little danger.
If the interior of the tube was dry before the ex-
plosion, it will be seen to be moist afterwards. The ^^ ^
liquid water which is formed occupies almost no space as
compared with the space occupied by the two gases before
combination. Now, if the experiment be performed with
the two gases in different proportions, it will be found that
only when they are mixed in the proportion of 2 volumes
of hydrogen to 1 volume of oxygen do they completely
disappear when exploded. If there is a larger proportion of
hydrogen present, the excess is left over. If there is a

66 THE ELEMENTS OF CHEMISTRY.

larger proportion of oxygen present, the excess of oxygen is
left over. Thus it is shown that when hydrogen and oxy-
gen combine to form water, they do so in the proportion of
2 volumes of hydrogen to 1 volume of oxygen.

Formation of Water by Passing Hydrogen over Heated
Oxides. — Water may be formed by passing hydrogen over a
compound containing oxygen and heating. A convenient
substance for the purpose is the compound of copper and
oxygen known as copper oxide or black oxide of copper.
It contains its elements in the proportion represented by
the formula CuO. At ordinary temperature hydrogen
does not act upon this substance. At a high temperature
the hydrogen combines with the oxygen, forming water,
and the copper is left behind as such. The reaction is
represented thus :

CuO + 2H = H20 + Ou.
Experiment 46. — Arrange an apparatus as shown in Fig. 21.

o

Fig. 21.

A is a Wolff's flask for making hydrogen. To remove impurities
the gas is passed through a solution of potassium permanganate
contained in the wash-cylinder B. The cylinder C contains con-
centrated sulphuric acid, and the U-shaped tube D contains gran-
ulated calcium chloride, both of them serving to remove moisture
from the gas. The pure dry hydrogen is now passed through the
hard glass tube Ey which contains a layer of copper oxide. After
the apparatus is filled with hydrogen the burner under E is

WATER. 57

lighted, and the copper oxide heated to low redness. Soon mois-
ture will be seen in the end of the tube and drops of water will
collect in the vessel 67.

How this Experiment Shows the Composition of Water. —

The copper oxide loses its oxygen and of course loses
weight. If, therefore, you should weigh the copper oxide
before the experiment, and afterward the copper, and
should also collect and weigh the water formed, you could
from the figures obtained easily calculate the relative weight
of oxygen contained in water, thus :

Let . x = weight of tube -f copper oxide before the experiment;

y = weight of tube + copper after the experiment.
Then x — y = weight of oxygen taken from the copper oxide.

The water formed is collected in a small tube containing
calcium chloride.

Let a = weight of calcium chloride tube before ;

b = weight of calcium chloride tube after.
Then b — a = weight of water formed.

If the experiment is carefully performed, it will be found

<£ y

that — — - is very nearly equal to f, which means that by

weight oxygen forms eight ninths of water.

Oxidation and Reduction. — Any substance which like
hydrogen has the power to abstract oxygen from com-
pounds containing it is called a reducing agent. The pro-
cess of abstracting oxygen from a compound is called re-
duction. Reduction and oxidation arc opposite processes.

Applications of the Heat Evolved by the Combination of
Hydrogen and Oxygen, — The heat evolved when hydrogen
combines with oxygen is very great, and it is utilized for
various purposes. To burn hydrogen in the air is, as we
have seen, a simple matter, but to burn it in oxygen re-

58 THE ELEMENTS OF CHEMISTRY.

quires a special apparatus to prevent the mixing of the
gases before they reach the end of the tube where the com
bustion takes place. The oxyhydrogen Mow-pipe answers
this purpose. It is simply a tube with a smaller tube pass
ing through it, as shown in Fig. 22.

Fig. 22.

The hydrogen is admitted through a and the oxygen
through b. It will be seen that they come together only
at the end of the tube. The hydrogen is first passed
through and lighted; then the oxygen is passed through
slowly, the pressure being increased until the flame ap-
pears thin and straight. It gives very little light, but it is
intensely hot.

Experiment 47. — Hold in the flame of the oxyhydrogen blow-
pipe successively a piece of iron wire, a piece of a steel watch
spring, a piece of copper wire, a piece of zinc, a piece of platinum
wire.

The Oxyhydrogen Blow-pipe Used in Working Platinum.—
The metal platinum is used for many purposes, particularly
for making chemical apparatus. The vessels are made
from molten platinum, and the metal is melted by means
of the oxyhydrogen blow-pipe.

The Lime-light or Drummond Light. — When the flame
of the oxyhydrogen blow-pipe is made to strike against
some substance which it cannot melt nor burn up, the
substance becomes heated so high that it gives off intense
light. The substance commonly used is quicklime.

WATER 59

Hence the light is generally called the lime-light. It is
also known as the Drummond light.

Experiment 48. — Cut a piece of lime of convenient size and
shape, say an inch long by three quarters of an inch wide and the
same thickness. Fix it in position so that the flame of the oxy-
hydrogen blow-pipe will strike upon it. The light is very bright,
but by no means as intense as the electric light.

Properties of Water. — Though, as we know, water is
widely distributed over the earth, we never find it perfectly
pure. All natural waters contain foreign substances in
solution. These substances are taken up from the air or
from the earth. Pure water is tasteless and inodorous.
In thin layers it is colorless, but in thick layers it is blue.
This has been shown in the laboratory by filling a long tube
with distilled water. When looked through it appears
blue. The beautiful blue color of some mountain lakes is
the natural color of pure water.

On cooling water contracts until it reaches the tempera-
ture of 4° C. At this point it has its maximum density.
When cooled below 4° it expands, and the specific gravity
of ice is somewhat less than that of water. Hence ice
floats on water.

Natural Waters. — The purest water found in nature is
rain-water, particularly that which falls after it has rained
for some time. That which first falls always contains im-
purities from the air. As soon as the rain-water comes in
contact with the earth and begins its course toward the
sea it begins to take up various substances, according to
the character of the soil with which it comes in contact.
Mountain streams which flow over rocky beds, particularly
beds of sandstone, which is very insoluble in water, contain
exceptionally pure water. Streams which flow over lim^

60 THE ELEMENTS OF CHEMISTRY.

stone dissolve some of the stone, and the water becomes
''hard." The many varieties of mineral springs have
their origin in the presence in the earth of certain sub-
stances which are soluble in water. Common salt occurs
in large quantities in different parts of the earth. As it is
easily soluble in water, many streams contain it; and as all
the streams find their way into the ocean, you see one
reason why the water of the ocean is salt.

Effervescent Waters are such as contain some gas,
usually carbonic-acid gas, in solution and give up a part of
it when placed in open vessels.

Chalybeate Waters contain some compound of iron.

Sulphur-water contains a compound of hydrogen and
sulphur, called hydrogen sulphide or sulphuretted hydrogen
(which see).

Impure Waters. — As streams approach the habitations of
man they are likely to become contaminated. The drain-
age from the neighborhood of human dwellings is very apt
to find its way into a near stream. This condition of things
is most strikingly illustrated by the case of a large town
situated on the banks of a river. It frequently happens
that the water of the river is used for drinking purposes,
and it also frequently happens that the water is contami-
nated by drainage. Water when once contaminated by
drainage tends to become pure again by contact with the
air in consequence partly of the action of the oxygen.
Hence river- water may become fit for use after having been
impure. If it is to be used for drinking purposes, however,
it is not well to rely too much upon this process of purifi-
cation.

Wells should not be dug too near dwellings and farm-
houses, as the drainage may find its way into them beneath

WATER.

61

the surface of the earth. This is a frequent source of
danger, as some diseases are communicated from one person
to another by means of contaminated drinking-water.

Distillation. — Water may be purified by means of distil-
lation. This consists in boiling the water, and then con-
densing the vapor by passing it through a tube which is
kept cool by surrounding it with cold water. By means of
distillation most substances in solution in water can be
got rid of. Substances which are volatile, however, will
of course pass over with the water vapor. Aboard ship salt
water is distilled and thus made fit for drinking. In chem-
ical laboratories ordinary water is distilled in order to purify
it for fine work with chemical substances. A simple ap-
paratus to illustrate the process of distillation is that shown
in Fig. 23.

Fig. 23.

The water to be distilled is placed in the flask A. The
flask is connected by means of a bent glass tube B with the
long tube CC. This in turn is surrounded by the larger
tube or jacket D. The side tube E is connected with a
faucet by means of the rubber tube G. The water is
allowed to flow slowly into the jacket and out at F> whence

62 THE ELEMENTS OF GHEM18TRT.

it passes through the rubber tube H to the sink. When
the water in A is boiled, the vapor passes into the tube CC.
Here it is cooled down, and takes the form of liquid, which
runs down and collects in the flask K called the receiver.
The apparatus therefore consists of three parts : the distil-
liiig-jlask, the condenser, and the receiver.

Experiment 49. — Dissolve some copper sulphate, or some other
colored substance, in a litre of water, and distil the water.

Uses of Water in Chemistry. — Water is the best solvent.
A greater number of substances dissolve in it than in any-
other liquid. Chemical operations are frequently carried
on in solution. That is to say, the substances which are
to act chemically upon one another are first brought into
solution. The object of this is to get the substances into
as close contact as possible. If we rub two solids together,
the particles remain separated by sensible distances, no
matter how finely the mixture may be powdered. If, how-
ever, the substances be dissolved and the solutions poured
together, the particles of the liquid move so freely among
one another that they come in intimate contact, thus aiding
chemical action. In some cases substances which do not
act upon one another at all when brought together in dry
condition act readily when brought together in solution
(Experiments 8 and 9.)

Solution. — In a solution the particles of the solid dis-
solved are in some way attracted and held in combination
by the particles of the liquid. There is a limit to the
amount of any substance which can be held in solution at a
given temperature. The substance dissolved is distributed
uniformly through the solution, no matter how dilute or
how concentrated the solution may be, provided it has stood
long enough, or has been thoroughly mixed by stirring,

WATEB. 63

In representing by an equation a reaction which takes
place between substances in solution, it is not customary to
take account of the water which acts as a solvent.

Summary. — You have thus learned that

(1) Water can be decomposed into hydrogen and oxygen
by means of an electric current;

(2) The gases are obtained in the proportion of eight
parts by weight of oxygen to one part by weight of hydro-
gen, or one volume of oxygen to two volumes of hydrogen;

(3) When hydrogen is burned water is formed;

(4) When hydrogen and oxygen are mixed together they
do not combine under ordinary circumstances;

(5) When a spark or flame is brought in contact with
the mixture, violent action accompanied by explosion takes
place;

(6) The action is caused by the chemical combination of
the two gases;

(7) They combine in the same proportions as those in
which they are obtained from water by the action of the
electric current;

(8) Water can be made by passing hydrogen over heated
copper oxide;

(9) By weighing the copper oxide before and after the
experiment, and determining the weight of the water
formed, the proportion of water which consists of oxygen
is found to be eight ninths.

Formula of Water. — All the facts taken together prove
that the composition of water is what it has been stated to
be. Now, using the accepted combining weights of hydro-
gen and oxygen, viz., 1 and 16, the simplest formula which
expresses the composition of water is H20. This expresses
the fact that water is composed of 2 parts by weight of

64 THE ELEMENTS OE CHEMISTS Y.

hydrogen and 16 parts by weight of oxygen, or 1 part of
the former to 8 parts of the latter. If 8' were adopted as
the combining weight of oxygen the formula of water would
be HO.

Comparison of Hydrogen and Oxygen. — Hydrogen and
oxygen are different kinds of matter, just as heat and elec-
tricity are different kinds of energy. Heat can be con-
verted into electricity, and electricity into heat, but one
element cannot by any means known to us be converted
into another. They appear to be entirely independent of
each other. If we compare hydrogen with oxygen we find
very few facts which indicate any analogy between the two
elements. In their physical properties they are, to be sure,
similar. Both are transparent, colorless, inodorous gases.
On the other hand, oxygen combines readily with a large
number of substances with which hydrogen does not com-
bine. Oxygen, as you have seen, combines easily with car-
bon, sulphur, phosphorus, and iron. It is a difficult matter
to get any of these elements to combine directly with hy-
drogen. Further, it is a general truth that substances
which combine readily with hydrogen do not combine read-
ily with oxygen. The two elements have opposite chemi
cal properties. What one can do the other cannot do.

Opposite Chemical Properties are Favorable to Combina-
tion.— Not only do hydrogen and oxygen, with their oppo-
site properties, combine with great ease under the proper
conditions, but, as we shall see later, it is a general rule
that elements of like properties do not readily combine
with one another, while elements of unlike properties do
readily combine with one another.

Ozone. — When electric sparks are passed for a time
through oxygen it is changed in a remarkable way. It ac-

WATER 65

quires a strong odor and is much more active than the
substance which we call oxygen. The odor of the gas is
noticed in the neighborhood of an electric machine in ac-
tion, and is said to be noticed during thunder-storms. The
substance which has the odor is ozone. It is formed in a
number of chemical reactions, as when phosphorus acts on
air in the presence of water. By cold and pressure it
has been obtained in the form of a dark-blue liquid. Ozone
is present in small quantities in the air.

Relation between Oxygen and Ozone. — When a certain
volume of oxygen is converted into ozone the volume of
gas is decreased to two thirds.

By heating ozone above 300° C. it is converted into ordi-
nary oxygen, and its volume increased from two to three.

It is clear that the element oxygen can be converted into
something else without the addition of anything to it.
This might lead you to think that it is not an element.
But the substance formed from it has exactly the same
weight and can be changed back to oxygen without any-
thing being added to it. It follows that the change must
take place within the oxygen itself.

Hydrogen Dioxide, H202. — Besides water, hydrogen and
oxygen form a second compound with each other. This is
hydrogen dioxide, H202O* It is prepared by treating ba-
rium dioxide, Ba02, with sulphuric acid. It is a liquid
which decomposes easily into water and oxygen. The ease
with which it gives up oxygen makes it a good oxidizing
agent. It is now manufactured on a large scale, and is
used in medicine.

* The reason for writing this formula H202 and not HO will he
seen later.

66 THE ELEMENTS OF CHEMISTRY.

CHAPTER IX.

COMPOUNDS OP NITROGEN WITH HYDROGEN AND
OXYGEN.

Destructive Distillation of Animal and Vegetable Sub-
stances which Contain Nitrogen. — Whenever a compound
containing carbon, hydrogen, and nitrogen is heated in a
closed vessel, so that the air cannot reach it, and it cannot
burn up, the nitrogen passes out of the compound, not as
nitrogen, but in combination with hydrogen, as ammonia.
Nearly all animal substances contain carbon, hydrogen,
oxygen, and nitrogen, and many of them give off ammo-
nia when heated in the way described. Heating in this
way is called destructive distillation. Similarly, com-
pounds containing carbon, oxygen, and hydrogen, even
though they be thoroughly dry, when heated give off oxy-
gen in combination with hydrogen as water (see Experi-
ment 1). The coal which is used for making illuminating-
gas contains some hydrogen and nitrogen in chemical com-
bination, and when the coal is heated in a closed vessel
ammonia is given off.

Natural Decomposition of Animal and Vegetable Sub-
stances which Contain Nitrogen. — The decay or slow nat-
ural decomposition of r.nimal and vegetable substances ex-
posed to the air is familiar to every one. It is caused by the
action of hosts of minute living things (called microbes) act-
ing together with the oxygen of the air. Some animal sub-
stances give off ammonia when they decompose in the air.

COMPOUNDS OF NITROGEN. 67

When animal substances decompose under proper condi-
tions either a nitrite or a nitrate is formed; the former is
derived from nitrous acid, HN02, the latter from nitric
acid, HN03. In some countries where the conditions are
favorable to the process immense quantities of nitrates are
found, chiefly potassium nitrate or saltpetre, KN03, and
sodium nitrate or Chili saltpetre, NaN03, so called because
it is found in Chili in large quantities. From the nitrates
nitric acid can easily be obtained.

How Compounds of Nitrogen are Made. — The principal
compounds of nitrogen are those which it forms with hy-
drogen and oxygen. They are made either from ammonia
or nitric acid by methods which will be described.

Ammonia, NH3. — The conditions under which ammonia
is formed have been mentioned. The chief source at pres-
ent is the "ammoniacal liquor" of the gas-works, which is
the water through which the gas has been passed for the
purpose of removing the ammonia. By adding hydro-
chloric acid to this liquid ammonium chloride, commonly
called sal ammoniac, is formed. This is the most common
compound containing ammonia, and it is therefore used in
the laboratory for making ammonia.

Preparation of Ammonia.

Experiment 50. — To a little ammonium chloride on a watch-
glass add a few drops of a strong solution of caustic soda, and
notice the odor of the gas given off. Do the same thing with
caustic potash. Mix small quantities of quicklime and ammonium
chloride in a mortar, and notice the odor. Has ammonium chlo-
ride this odor ?

To prepare ammonia mix slaked lime and ammonium
chloride in the proportion of 2 parts of the former to 1 part
of the latter, and gently heat the mixture. It has been
shown that besides the ammonia, which is given off in the

68

THE ELEMENTS OF CHEMISTBY.

form of gas, calcium chloride, CaCl2, and water are formed
in the reaction. It is represented thus:

2NH401 + 0a02H2 = 2NH3 + CaCl2 + 2H20.
Experiment 51. — Arrange an apparatus as shown in Fig. 24.

Fig. 24.

In the flask put a mixture of 100 grams slaked lime and 50 grams
ammonium chloride. Heat on a sand-bath. After the air is
driven out, the gas will be completely absorbed by the water in
the first Wolff's flask. Disconnect at A, and connect with another
tube bent upward. Collect some of the escaping gas by displac-
ing air, placing the vessel with the 'mouth downward, as the gas
is much lighter than air. The arrangement is shown in Fig.
25. The vessel in which the gas is collected
should be dry, as water absorbs ammonia very
readily. Hence also it cannot be collected over
water. In the gas collected introduce a burning
stick or taper. Does the gas burn? Does it
support combustion ? In working with the gas
great care must be taken to avoid breathing it in
any quantity. After enough has been collected,
connect the delivery- tube again with the series
of Wolff's flasks, and pass the gas through the
Fig. 25. water as long as it is given off.

Properties of Ammonia. — Prom the observations made in
the experiment just performed you see that ammonia is a

COMPOUNDS OF NITROGEN. 69

colorless, transparent gas. It has a very penetrating char-
acteristic odor. In concentrated form it causes suffocation.
It is but little more than half as heavy as air. It is easily
compressed to the liquid form by pressure and cold. When
the pressure is removed from the liquefied ammonia it
passes back to the form of gas. In so doing it absorbs
heat. These facts are taken advantage of for the artificial
preparation of ice. Carre's ice-machine is used for this
purpose. Ammonia does not burn in the air, but does burn
in oxygen. It is absorbed by water in very large quantity.
One volume of water at the ordinary temperature dissolves
about 600 volumes of ammonia-gas, and at 0° C. about 1000
volumes.

Spirits of Hartshorn. — The solution of ammonia in water
is what we commonly have to deal with under the name
ammonia. In ordinary language it is called "spirits of
hartshorn."" The solution loses all its gas when heated to
the boiling temperature.

Nitric Acid, HN03. — To effect the direct union of nitro-
gen with oxygen and hydrogen is not easier than to effect
the direct union of nitrogen and hydrogen to form ammo-
nia. The silent and continuous action of minute living
things in the soil is always tending to transform the waste
products of animal life into compounds closely related to
nitric acid. In general, by oxidation the nitrogen of ani-
mal substances is converted into nitric acid, while by re-
duction it is converted into ammonia.

Preparation of Nitric Acid. — Nitric acid is obtained from
a nitrate like potassium nitrate, K]ST03, or sodium nitrate,
NaN"Os, by treating with sulphuric acid.

2Na^03 + H2S04 = Na2S04 + 2HNO,.

Sodium - sulphuric . sodium , nitric

nitrate ana acid gl e sulphate ana acid.

70

THE ELEMENTS OF CHEMISTRY.

You see that the hydrogen of the sulphuric acid changes
place with the sodium of the nitrate.
Experiment 52. — Arrange an apparatus as shown in Fig. 26.

Fig. 26.

In the retort put 25 grams sodium nitrate (Chili saltpetre) and
1 5 grams concentrated sulphuric acid. On heating gently, nitric
acid will distil over and be condensed in the receiver. In the
latter stage of the operation the vessel becomes filled with a red-
dish-brown gas. The acid which is collected has a somewhat
yellowish color.

Pure Nitric Acid is a colorless liquid. It gives off color-
less fumes when exposed to the air. When boiled it under-
goes slight decomposition into oxygen, water, and compounds
of nitrogen and oxygen. One of these compounds is col-
ored, and it is this which is noticed in the last experiment
and whenever strong nitric acid is boiled. Nitric acid
suffers a similar decomposition when exposed to the action
of thD direct rays of the sun. In consequence of this de-
composition bottles containing strong nitric acid sometimes

COMPOUNDS OF NITBOGEN. 71

contain a reddish-brown gas above the liquid after standing
for some time. Strong nitric acid acts violently on many
substances, particularly those of animal and vegetable
origin, decomposing them. It causes bad wounds in con-
tact with the flesh; it eats through clothing ; it burns
wood; it dissolves metals; and it is altogether one of the
most active of chemical substances. In working with it it
is necessary to take the greatest care.

Ordinary or Commercial Nitric Acid contains only about
68 per cent of the chemical compound H1SJ~03. The rest
is mostly water, though there are several impurities present
in small quantities.

How to Make Strong Nitric Acid.*— Pure, strong nitric
acid may be made by mixing commercial nitric acid and
commercial strong sulphuric acid and distilling.

Experiment 53. — Mix together 400 grams ordinary concen-
trated sulphuric acid and 80 grams ordinary concentrated nitric
acid. Distil the mixture from a retort arranged as in Experiment
52, taking care to keep the neck of the retort cool by placing filter-
paper moistened with cold water on it. Use the acid thus ob-
tained for the purpose of studying the properties of pure nitric
acid.

Nitric Acid Gives up Oxygen Readily. — Nitric acid is
much used on account of the ease with which it gives up
oxygen. Many substances burn up in strong nitric acid.

Experiment 54. — Pour concentrated nitric acid into a wide test-
tube, so that it is about one fourth filled. Heat the end of a stick
of charcoal of about the size of a lead-pencil, and, holding the
other end with a forceps, introduce the heated end into the acid.
It will continue to burn with a bright light, even though it be

* The experiments with strong nitric acid may be performed or not
as the teacher thinks best They had better not be performed by the
pupils, and should not be performed by any one who is not experi-
enced in working with chemical substances.

72

THE ELEMENTS OF CHEMISTBY.

placed below the surface of the liquid. The action is oxidation.
The charcoal in this case finds the oxygen in the acid and not in
the air. Great care must be taken in performing this experiment.
The charcoal should not come in contact with the sides of th
test-tube. A large beaker-glass should be placed beneath tb
test-tube, so that in case the tube should break, the acid woulc
be caught and prevented from doing harm. The arrangement o:
the apparatus is shown in Fig. 27. The gases given off from the

Fig. 27.

tube are offensive and poisonous. Hence this as well as all other
experiments with strong nitric acid should be carried on either
out of doors or under a hood in which the draught is good.

Experiment 55. — In a small flask put a few pieces of granulated
tin. Pour on this just enough strong nitric acid to cover it.
Heat gently over a small flame. What takes place ? What is the
appearance of the substance left in the flask ? It is mostly a com-
pound of tin and oxygen. (See Experiment 7.)

Action of Nitric Acid upon Some Metals. — Generally when
an acid acts upon a metallic element like silver, copper,
lead, etc., the hydrogen of the acid is liberated and the
metallic element takes its place. Thus when nitric acid

COMPOUNDS of nitbogen: 73

acts upon silver the action takes place as represented in the
equation

Ag + HN03 = AgN03 + H.

Silver and ■** give ^^ and hydrogen.

The substances thus formed are called nitrates. At the
same time the hydrogen and a part of the oxygen are taken
out of the acid, and compounds of nitrogen and oxygen are
formed which are represented by the formulas N02, NO,
and N20. The first of these, nitrogen peroxide, N02, is a
colored gas, and as some of it is always formed when nitric
acid acts upon metals in the air, the presence of the red-
dish-brown gas observed in the experiments already per-
formed with nitric acid will be readily understood.

Experiment 56. — Dissolve a few pieces of copper-foil in ordi-
nary commercial nitric acid diluted with about half its volume of
water. The operation should be carried on in a good-sized flask
and either out of doors or under a good hood. What action takes
place ? After it is over what is the appearance of the liquid in
the flask ? Pour it out and evaporate to crystallization. Com-
pare the substance thus obtained with copper nitrate. — Heat
specimens of each. — Treat small specimens with sulphuric acid.—
Do the substances appear to be identical ? What reasons have
you for considering them identical ?

Aqua Regia is made by mixing together concentrated
nitric and hydrochloric acid. It is an excellent solvent.
It is called aqua regia because it dissolves the king of
metals, gold. Similarly nitric acid is called aquafortis, or
strong water. In olden times all liquids were regarded as
kinds of water, and all gases as kinds of air.

The Oxides of Nitrogen. — Nitrogen combines with oxygen
in five proportions. The names and symbols of the com-
pounds formed are here given.

74 THE ELEMENTS OF CHEMISTRY.

Nitrous oxide " N20

Nitric oxide , NO or N202

Nitrogen trioxide T$209

Nitrogen peroxide N02 or N204

Nitrogen pentoxide N206

A Good Illustration of the Law of Multiple Proportions.—

The combining weight of nitrogen being 14, the above sym-
bols represent the fact that in the compounds of nitrogen
and oxygen the quantities of . oxygen combined with 28
parts of nitrogen are 16, 32, 48, 64, and 80 ; or 16, twice
16, three times 16, four times 16, and 5 times 16 parts of
oxygen are combined with 28 parts by weight of nitrogen
This series of compounds is an excellent illustration of the
law of multiple proportions, which is one of the most im
portant and interesting truths of chemistry. — [What is the
law of multiple proportions? How does this series illus-
trate it?]

Nitrous Oxide, N20. — This compound is formed by reduc-
tion of nitric acid when the acid acts upon metals under
favorable conditions of concentration and temperature. It
is usually prepared by heating ammonium nitrate. The
decomposition takes place as represented, thus:

NH4N03 = • N20 + 2H20

A*Sto*T heated gives "S and ™ter'
Experiment 57. — In a retort heat 10 to 15 grams crystallized
ammonium nitrate until it has the appearance of boiling. Do not
heat higher than is necessary to secure a regular evolution of gas..
Connect a wide rubber tube directly with the neck of the retort,
and collect the gas over water, as in the case of oxygen.

Properties of Nitrous Oxide. — It is colorless and transpar-
ent and has a slightly sweetish taste. When inhaled it
causes a kind of intoxication, which is apt to show itself
in the form of hysterical laughing. Hence the gas is com-

COMPOUNDS OF NimOGEN.

75

monly called laughing-gas. Inhaled in larger quantity it

causes unconsciousness and insensibility to pain. It is

therefore used in certain surgical operations, particularly in

pulling teeth. It supports combustion almost as well as

pure oxygen.

Experiment 58. — Insert into it a piece of burning wood, a can
die, and a small piece of phosphorus.

Nitric Oxide, NO. — This gas, as has been stated, is

formed when nitric acid acts upon some metals, as copper.

It seems probable that two changes take place:

(1) The copper displaces the hydrogen of the acid, and
copper nitrate is formed; and

(2) The hydrogen acts upon the nitric acid, reducing it
and forming nitric oxide.

These two stages may be represented thus:

2HN03 + Ou = Cu(N03)Q + 2H;

and copper give ^?2SL and hydrogen;

Nitric
acid

2HN03 + 6H = 4H,0 + 2NO.

and

Nitric
acid

and hydrogen give water and

nitric
oxide.

Experiment 59. — Arrange an apparatus as shown in Fig. 28.
In the flask put a few pieces of copper-foil. Cover
this with water. Now add slowly, waiting each
time, ordinary concentrated nitric acid. When
enough acid has been added gas will be given off.
If the acid is added quickly it not infrequently
happens that the evolution of gas takes place too
rapidly, so that the liquid is forced out of the flask
through the funnel-tube. This can be avoided by
not being in a hurry. What is the color of the gas
in the flask at first ? What is it after the action
has continued for a short time ? Collect over
water two or three vessels full.

Properties of Nitric Oxide. — Nitric oxide is

a colorless, transparent gas. Its most re- fig. 2&

76 THE ELEMENTS OF CHEMISTRY.

markable property is its power to combine directly with
oxygen when the two are brought together. The reaction
is represented by the equation

NO + 0 = NO,2.

The product is nitrogen peroxide, and this at ordinary
temperatures is a reddish-brown gas.

Experiment 60. — Turn one of the vessels containing colorless
nitric oxide with the mouth upward and uncover it. What takes
place ? Explain the appearance of the colored gas in Experiment
59, and the fact that it afterward disappeared. What was in the
vessel at the beginning of the operation ? Bo not inhale the gas,
Perform the experiment with nitric oxide where there is a good
draught.

Experiment 61. — Into one of the vessels containing nitric ox-
ide insert a burning candle. Does the gas burn ? Does it sup-
port combustion ?

Nitric oxide does not burn and does not support com-
bustion.

Nitrogen Peroxide, N02. — This is the reddish-brown gas
formed in the experiments with nitric oxide. It has a dis-
agreeable smell and is poisonous. It is used in large quan-
tities in the manufacture of the extremely important sub-
stance sulphuric acid, as will be explained farther on.

CHLOBINE AND ITS COMPOUNDS. 77

CHAPTEE X.

CHLORINE AND ITS COMPOUNDS WITH HYDROGEN
AND OXYGEN.

Introductory. — A little later you will see that oxygen
and nitrogen are members of families of elements. The
other members of the oxygen family resemble oxygen in
many respects, and the other members of the nitrogen
family resemble nitrogen. Hydrogen, strange to say, does
not belong to any family but stands by itself. Another
family is the chlorine family, of which chlorine is the best-
known member.

Occurrence of Chlorine. — Chlorine, though widely dis-
tributed in nature, does not occur in very large quantity as
compared with oxygen and hydrogen. It is found chiefly
in combination with the element sodium as common salt
or sodium chloride, which is represented by the symbol
NTaOl. It is also found in combination with other ele-=
ments, as potassium, magnesium, etc. In small quantity
it occurs in combination with silver, forming one of the
most valuable silver ores. All the chlorine with which we
have to deal is made from common salt.

Preparation of Chlorine. — We cannot decompose sodium
chloride directly into its elements. In order to get the
chlorine out of the compound in the free state it is neces-
sary first to get it in combination with hydrogen in the
form of hydrochloric acid, HOI This is very easily ac-

78 THE ELEMENTS OF CBEMISTKY.

complished by treating salt with ordinary sulphuric acid«
The reaction is represented thus:

(1) 2NaCl + H2S04 = Na2S04 + 2HC1.

Sodium OTw1 sulphuric _._ A sodium _, hydrochloric
chloride and acid Slve sulphate and acid.

As you see, the sodium of the salt and the hydrogen of
the sulphuric acid exchange places, a kind of action which
is very common. [How does the process for making nitric
acid resemble this process?] Now, if hydrochloric acid be
brought in contact with a substance which gives up oxygen
easily, the hydrogen will unite with the oxygen to form
water, and the chlorine will be set free. The reaction is
represented thus:

(2) 2HC1 + 0 = HaO + 2a

In the laboratory it is most convenient to bring together
ordinary hydrochloric acid and manganese dioxide, Mn02,
a substance which you have already had to deal with in
preparing oxygen. The action which takes place is repre-
sented thus:

Mn02 + 4HC1 = MnCl, + 2HaO + 201.

Commercial Manufacture of Chlorine. — Chlorine is an im»
portant article of commerce, as it finds extensive use for
bleaching and disinfecting. As manganese dioxide is a
comparatively expensive substance, efforts have been made
to devise some cheaper method of preparation than that
just mentioned. Two are in use.

(1) Deacon's Process. — This consists in passing air and
hydrochloric acid together through a heated tube contain-
ing clay balls which have been saturated with a solution of

CHLOBINE AND ITS COMPOUNDS.

79

copper sulphate or blue vitriol. Exactly why the oxida-
tion should take place under these circumstances is not
known. The main part of the action is the oxidation of
the hydrochloric acid, as represented in equation (2) above.
(2) Weldon's Process. — This consists, in the first place,
in making the chlorine from manganese dioxide and hy-

Fig. 29.

drochloric acid, and then, instead of throwing away the
liquid contained in the vessel, mainly manganese chloride,
MnCl2, in solution, this is treated with steam, lime, and
air, and thus converted into a substance which acts towards
hydrochloric acid like manganese dioxide, setting chlorine
free.

80 THE ELEMENTS OF CHEMISTRY.

Experiment 62. — In a flask put about 100 grams (3 to 4
ounces) of black oxide of manganese. Pour upon it enough
ordinary concentrated hydrochloric acid to cover it completely.
Arrange the apparatus as shown in Fig. 29. Heat gently in a
sand-bath, when chlorine will be given off. Collect six or eight
dry cylinders or bottles full of chlorine by letting the delivery-
tube extend to the bottom of the collecting vessel and covering
the mouth of the vessel with a piece of paper. You can see when
the vessel is full by the color of the gas. — The experimmts witl
chlorine should be carried on in a place where the draught %
good. Do not inhale the gas.

(1) Into one of the vessels containing chlorine introduce a little
finely powdered antimony. The two elements combine at once
with evolution of light and heat. [In what respects does this ex-
periment resemble the one in which iron was burned in oxygen t~

(2) Into a second vessel introduce a few pieces of heated cop-
per-foil. Combination takes place with evolution of light and
heat. A compound ot copper and cmorine is formed.

(3) Into a third vessel introduce a piece of paper with writing
on it, some flowers, and pieces of colored calico. Most of the
colors will be destroyed if the substances are moist.

(4) Into a fourth vessel introduce a dry piece of the same
colored calico as that used in (3). The dry piece is not bleached;
the moist piece is.

Properties of Chlorine. — Chlorine is a greenish-yellow
gas. It has a disagreeable smell, and acts upon the pas-
sages of the throat and nose, causing irritation and inflam-
mation. The feeling produced is much like that of "a
cold in the head." Inhaled in concentrated form, that is,
not diluted with a great deal of air, it would cause death.
It is much heavier than air. Its specific gravity is 2.45.
A. litre of chlorine gas at 0° C. and atmospheric pressure
weighs 3.167 grams. It is soluble in water and acts upon
mercury, and therefore must be collected by displacement
of air. It combines readily with other substances and de*
stroys colors or bleaches. It is one of the most active ele-
ments. In bleaching it decomposes the colored substances

CHLORINE AND ITS COMPOUNDS. 81

and forms colorless substances. It is used to disinfect sub-
stances.

Disinfection. — Substances given off from persons sick
with some diseases, such as typhoid fever, small-pox, etc.,
are apt to cause the same diseases in well persons. It is
therefore desirable to destroy them. This is called disin- ,
fecting. One of the most valuable substances for this
purpose is chlorine. It is sold in the form of "bleaching
powder," known also as "chloride of lime," which is a
compound made by passing chlorine gas into slaked lime.
A solution of this substance in water is a valuable disin-
fectant. Old drains, sinks, etc., from which bad odors
arise may be purified by adding enough of such a solu-
tion.

Combination of Hydrogen and Chlorine. — Just as hydro-
gen burns in the air it burns also in chlorine.

Experiment 63. — Light a jet of hydrogen in the air and care-
fully introduce it into a vessel containing chlorine. Does it con-
tinue to burn ? What is the appearance of the flame ? What
evidence have you that a product is formed ? Test the gas remain-
ing in the jar with blue litmus solution shaken up in it, and com-
pare with the action of chlorine-gas on the solution.

The burning of hydrogen in air or oxygen is, as you
have seen, simply the act of combination of hydrogen and
oxygen, the product being water in the state of vapor, and
therefore invisible. When hydrogen burns in chlorine the
action consists in the union of the two gases, the product
being hydrochloric acid, HC1, which forms clouds in the
air. In both cases the action is accompanied by heat and
light.

Chlorides. — Just as the compounds of oxygen with other
6

82 THE ELEMENTS OF CHEMISTRY.

elements are called oxides, so the compounds of chlorine
with the elements are called chlorides.

Hydrochloric Acid, HC1. — The only compound which
chlorine and hydrogen form with each other is hydrochloric
acid. It has already been shown that hydrogen burns in
chlorine, and that hydrochloric acid is formed. The two
gases may be mixed together and allowed to stand together
indefinitely in the dark, and no action will ta"ke place. If,
however, the mixture be put in a room lighted by the sun,
but where the sun does not shine directly upon it, combina
tion takes place gradually; and if the sun be allowed to
shine upon the mixture for an instant, explosion occurs,
and this is the sign of the combination of the two gases
The same sudden combination is effected by applying a
flame or spark to the mixture. In this case light causes
chemical action. The art of photography depends upon the
fact that light has the power to cause chemical changes, as
will be more fully explained later. It should be specially
noted that the cause of the chemical changes in the cases
referred to is not the heat but the light. If the substances
are heated to the same temperature in the dark, the
changes do not take place.

Preparation of Hydrochloric Acid.

Experiment 64. — Pour 2 or 3 c. cm. concentrated sulphuric acid
on a gram or two of common salt in a test-tube. What takes
place ? Is a gas given off ? What is its appearance ?

Hydrochloric acid is always made by treating common
salt with sulphuric acid, when the reaction takes place which
is represented in the equation

SNaCl + H2S04 = Na2S04 + 2H01.

The products are sodium sulphate and hydrochloric acid.

CHLORINE AND ITS COMPOUNDS. 83

The hydrochloric acid is given off as a gas, and the sodium
sulphate remains behind in the flask.

Experiment 65. — Arrange an apparatus as shown in Fig. 24,
page 68. Weigh out, separately, 100 grams common salt, 100
grams concentrated sulphuric acid, and 1 part water. Mix the
acid and water, taking the usual precautions (see note p. 47).
Let the mixture cool down to the ordinary temperature ; and
then pour it on the salt in the flask. Now heat the flask gently,
and the gas will be regularly given off. Conduct it at first
through water contained in two or three Wolff's bottles until
what passes over is completely absorbed in the first Wolff's bottle.
The reason why gas at first bubbles through all the bottles is that
the apparatus is full of air, which is first driven out. When the
air has been displaced, the gas is all absorbed as soon as it comes
in contact with the water. — After the gas has passed for ten to
fifteen minutes disconnect at A (see Fig. 24). Notice the fumes.
These become denser by ' ' blowing the breath" upon them. Apply
a lighted match to the end of the tube. Does the gas burn ?
Collect some of the gas in a dry cylinder by displacement of air,
as in the case of chlorine. The specific gravity of the gas being
1.26, the vessel must of course be placed with the mouth upward.
Has the gas any color? Is it transparent? — Insert a burning
stick or candle in the cylinder filled with the gas. Does the gas
support combustion ? — Connect the generating-flask again with
the bottles containing water, and let the process continue until no
more gas comes over. The reaction represented in the equation

2NaCl + H2S04 = Na2S04 + 2HC1

is now complete. After the flask has cooled down pour water
on the contents, and when the substance is dissolved filter it and
evaporate to such a concentration that, on cooling, the sodium
sulphate is deposited. Pour off the liquid, and dry the solid sub-
stance by placing it upon folds of filter-paper. Compare the sub-
stance with the common salt which you put in the flask before
the experiment. What proofs have you that the two substances
are not the same? Heat a small piece of each in a dry tube
closed at one end. What differences do you notice ? — Treat a small
piece of each in a test-tube with sulphuric acid. What difference
<lo you notice? — If in the experiment you should recover all the
sodium sulphate formed, how much would you have ? [The com-

84 THE ELEMENTS OF CHEMISTRY.

bining weight of sodium is 23; of sulphur 32; and of chlorine
35.5.] The relations between the quantities of the substances
which take part in the reaction are expressed as follows:

2NaCl + H2S04 = NaaSO*

2(23 +35.5) +2x1 + 32 + 4x16 2x23 + 32 + 4x16

117 parts + 98 parts = 142 parts

+ 2HC1.

2(1 + 35.5).

+ 73 parts.

The quantity of sodium sulphate formed is to the quantity of
sodium chloride as 142 is to 117. Therefore if you use 100 grams
of sodium chloride, the quantity of sodium sulphate formed is
found by solving the simple proportion

117 : 100 :: 142 : grams of sodium sulphate.

— Put about 50 c.cm. of the liquid from the first Wolff's bottle in
a porcelain evaporating-dish. Heat over a small flame just to
boiling. Is hydrochloric acid given off ? Can all the liquid be
driven off by boiling ? — Try the action of the solution on some
iron filings. Is a gas given off ? What is it ? — Add some to a
little granulated zinc in a test-tube. Is hydrogen given off ? —
Add some to a little manganese dioxide in a test-tube. Is chlo-
rine given off ? — Add ten or twelve drops of the acid to 2 or 3
c. cm. water in a test-tube. Taste the dilute solution. How would
you describe the taste ? — Add a drop or two of a solution of blue
litmus, or put into it a piece of paper colored blue with litmus.
Litmus is a vegetable color prepared for use as a dye. Other
vegetable colors are changed by hydrochloric acid. — The color will
be restored by adding a few drops of caustic soda or ammonia.

Composition of Hydrochloric Acid. — That hydrochloric
acid consists of hydrogen and chlorine is shown by the fact
that it is formed when hydrogen combines with chlorine. It
has further been shown that when the two gases combine
they do so in equal volumes, 1 volume of hydrogen com-
bining with 1 volume of chlorine; and these 2 volumes form
2 volumes of hydrochloric acid gas. In 36.5 parts by

CHLORINE AND ITS COMPOUNDS. 85

weight of hydrochloric-acid gas there are contained 1 part
by weight of hydrogen and 35.5 parts by weight of chlorine.
The combining weight of chlorine being 35.5, the composi-
tion of hydrochloric acid gas is represented by the symbol
HOI.

Chemical Conduct of Hydrochloric Acid. — 1 . Hydrochlo-
ric acid gives up its hydrogen when brought in contact
with certain substances like iron, zinc, etc., which belong
to the class called metals; and takes up these metallic ele-
ments in place of the hydrogen. Thus zinc and hydro-
chloric acid give zinc chloride and hydrogen:

Zn + 2HC1 = ZnCl2 + 2H.

2. In contact with substances which give up oxygen, or
with oxygen itself under certain, circumstances, it gives up
its chlorine, while the hydrogen combines with oxygen to
form water :

2HC1 + 0 = H20 + 201.

3. When it acts upon metallic oxides or compounds of
the metals with oxygen, such as magnesia or magnesium
oxide, MgO; lime or calcium oxide, CaO; zinc oxide,
ZnO, etc., — compounds which do not easily give up their
oxygen, — the hydrogen of the acid combines with the oxy-
gen of the oxide to form water, while the metals combine
with the chlorine:

MgO + 2HC1 = MgCl2 + H20;
CaO + 2HC1 = CaCl2 + H20;
ZnO + 2HC1 = ZnCl2 + H20.

Compounds of Chlorine with Oxygen and with Hydrogen
and Oxygen.— As you have seen, chlorine combines very

86 THE ELEMENTS OF CHEMISTRY.

readily with hydrogen, and hydrogen with oxygen, and the
products are stable compounds. On the other hand, chlor-
ine does not combine directly with oxygen. Indirectly the
two elements can be made to combine, but the compounds
decompose very easily into the elements.

Compounds of Chlorine with Hydrogen and Oxygen. — The
principal reaction made use of for the preparation of com-
pounds of chlorine, oxygen, and hydrogen consists in treat-
ing caustic potash or potassium hydroxide, KOH, with
chlorine. If the solution of caustic potash is warm and
concentrated the reaction takes place mainly as represented
in this equation:

6KOH + 6C1 = 5KC1 + KC103 + 3H20.

The compound KC1 is potassium chloride ; K0103 is the
well-known substance potassium chlorate or chlorate of
potash, used for making oxygen in Experiments 20 and 21.

If the solution is dilute the reaction takes place thus :

2KOH + 2C1 = KOI + KCIO + H20.

The product KCIO is known as potassium hypochlorite.

Hypochlorous Acid, HCIO, and Chloric Acid, HC103. —
Just as sodium nitrate, ISTaNOg, yields nitric acid, HNOa,
when treated with sulphuric acid (see Experiment 52); and
sodium chloride, NaCl, yields hydrochloric acid, HOI (see
Experiment 65); so potassium chlorate, KC103, yields
chloric acid, HC103; and potassium hypochlorite, KCIO,
yields hypochlorous acid, HCIO:

2NaN03 + H2S04 = 2HNO, + Na2S04;
2Na01 + H2S04 = 2HC1 + Na2S04; .
2KC103 + H2S04 = 2HC103 + K2S04;
2KC10 + H2S04 = 2HC10 + K2S04.

CHLOBINE AND ITS COMPOUNDS. 87

Bleaching-potvder or "chloride of lime" is a substance
similar to potassium hypochlorite, and is formed by passing
chlorine into slaked lime. It will be more fully considered
under calcium.

Other Compounds of Chlorine, Hydrogen, and Oxygen. —
There are four compounds of chlorine, hydrogen, and oxy-
gen. As far as composition is concerned, they bear a
simple relation to one another. Beginning with hydro-
chloric acid, we have a series of compounds the successive
members of which differ by one combining weight of oxy-
gen:

Hydrochloric acid HC1.

Hypochlorous acid . . HCIO.

Chlorous acid HC102.

Chloric acid HC103.

Perchloric acid HC104.

This series, like the series of compounds of nitrogen and
oxygen, illustrates very clearly the lata of multiple propor-
tions. [What is the law of multiple proportions? In what
way does this series illustrate the law ?]

Compounds of Chlorine and Oxygen. — There are three of
these compounds, viz. : chlorine monoxide, C120; chlorine
trioxide, C1203; and chlorine tetroxide, C102 (or C1204).
They are unstable substances which easily break up into
chlorine and oxygen. They are not easily prepared in pure
condition and are not well known.

88 THE ELEMENTS OF CHEMISTRY.

CHAPTEE XL
ACIDS— BASES— NEUTBALIZATION— SALTS.

Introduction. — You have already met with a number of
substances called acids. It is now time to inquire what
these substances haye in common which lead chemists to call
them all acids. What is there in common, for example, be-
tween the heavy, oily liquid sulphuric acid and the colorless
gas hydrochloric acid? It is not possible to understand the
nature of their common properties without reference to a
class of substances to which special attention will be called
in due time. These are the alkalies, which are the most
marked members of a class of substances known as bases.
Acids and bases have the power to destroy the characteristic
properties of each other. When an acid is brought in con-
tact with a base in proper proportions, the characteristic
properties of both the acid and the base are destroyed.
They are said to neutralize each other.

A Study of Neutralization. — The most common acids are
sulphuric, hydrochloric, and nitric acids. Among the
more common bases are caustic soda, caustic potash,
and lime. A convenient way to recognize whether a sub-
stance has acid or basic properties is by means of certain
color-changes. The dye litmus is blue. If a solution
which is colored blue with litmus be treated with a drop or
two of an acid, the color is changed to red. If now the
red solution be treated with a few drops of a solution of $

A CIDS— BASES— NEUTBALIZA TION— SALTS.

89

base, the blue color is restored. There are many other
substances which change markedly in color, according to
whether the solutions in which they are present are acid or
basic. An infusion of red cabbage, for example, changes
color when treated with an acid, and recovers its color
when again treated with an alkali.

Experiment 66. — Make dilute solutions of nitric, hydrochloric,
and sulphuric acids (1 part dilute acid, such as is used in the lab-
oratory, to about 50 parts of water); and of caustic soda and
caustic potash (about 5 grams to 100 c.cm. of water). Measure
off about 20 c.cm. of each of the acid solutions. Add a few drops
of a solution of blue litmus. Gradually add to each of the meas-
ured quantities of acid sufficient dilute caustic soda to cause the
red color just to change to blue. As long
as the solution is red it is acid. When it
turns blue it is alkaline. At the turning
point it is neutral. The experiment is
best performed with the aid of a burette
which is a graduated tube with an open-
ing from which small quantities can be
poured. A convenient shape is that rep-
resented in Fig. 30. At the lower end
is a small opening. The flow of the
liquid from the burette is controlled by
means of a small pinch-cock. It will re-
quire some practice to enable you to know
exactly when the red color disappears and
the blue appears, but with practice the
point can be recognized with great accu-
racy. Should too much alkali be allowed
to get into the acid, add a small measured
quantity of the acid from another burette.
In one experiment neutralize 20 c.cm. of
the acid; in a second 10 c.cm.; in a third
'15 c.cm.— What relation do the quantities
of alkali used bear to one another ?— Does it always require a
definite quantity of alkali to neutralize a certain quantity of
1 acid ?

90 THE ELEMENTS OF CHEMISTRY.

What is Formed when an Acid Neutralizes a Base ? — To

determine this we may use in larger quantities the same
substances as those used in the preceding experiments.

Experiment 67. — (1) Dissolve 10 grams caustic soda in 100 cc.
water. Add hydrochloric acid slowly, examining the solution
from time to time by means of a piece of paper colored blue
with litmus. As long as the solution is alkaline it will cause no
change in the color of the paper. The instant it passes the point
of neutralization it changes the color of the paper red. When
this point is reached, evaporate the water on a water-bath to com-
plete dryness, and see what is left. — Taste the substance. Has it
an acid taste ? Does it suggest any familiar substance ? If it is
common salt or sodium chloride, how ought it to conduct itself
when treated with sulphuric acid ? Does it conduct itself in this
way ? Is the substance an alkali ? Is it an acid ? Is it neutral ?
Its formation took place according to the equation

HC1 + JSTaOH = NaOl + H20.

2. Perform the same experiment, using nitric acid instead of
hydrochloric acid. — Compare the product with sodium nitrate.
Heat a small specimen of each in a tube closed at one end. What
takes place ? Treat a small specimen of each with a little sul-
phuric acid in test-tubes. What takes place? The reaction
between nitric acid and caustic soda is represented thus:

HN03 + NaOH = NaNO, + H20.

3. Similarly, sulphuric acid and caustic soda give sodium sul-
phate and water, thus :

H2S04 + 2NaOH = Na.SO* + 2HaO.

4. Similar reactions take place with caustic potash. Hydro-
chloric acid and caustic potash yield potassium chloride and water:

HC1 + KOH==KCl+H20.

Nitric acid and caustic potash yield potassium nitrate and water ;

HNOs + KOH = KN03 + H20.

Sulphuric acid and caustic potash yield potassium sulphate ancj
water :

H3S04 + 2KOH ==? K2S04 + 2HA

ACIDS-BASES— NEUTEALIZATION— SALTS. 91

What these Experiments Show. — Considering the facts
just learned, you see

(1) That an acid contains hydrogen;

(2) That a base contains a metal;

(3) That when an acid acts upon a base the hydrogen
and the metal exchange places;

(4) That the substance obtained from the acid by replac-
ing the hydrogen by a metal is neutral;

(5) That the substance formed by replacing the metal of
the base by hydrogen is water.

The Fourth Statement not General. — All these statements
except the fourth hold true of all cases. In some cases
after replacing the hydrogen of an acid by a metal the sub-
stance has an alkaline reaction; and in other cases the pro-
duct has an acid reaction.

Products Formed when a Metal Acts upon an Acid. — You
have already seen that hydrochloric acid and sulphuric acid
act upon certain metals, as iron and zinc, and that the
action consists in giving up hydrogen and taking up metal
in its place. The products of this action are the same in
character as those formed by the action of acids on
bases.

Acids, Bases, and Salts. — An acid is a substance contain-
ing hydrogen, which it easily exchanges for a metal when
treated with a metal itself, or with a compound of a metal
called a base.

A base is a substance containing a metal combined with
hydrogen and oxygen. It easily exchanges its metal for
hydrogen when treated with an acid.

The products of the action of an acid on a base are, first,
water, and, second, a neutral substance called a salt. In
the examples already given, sodium chloride, potassium

92 THE ELEMENTS OF CHEMISTRY.

chloride, sodium nitrate, potassium nitrate, sodium sul-
phate, and potassium sulphate are salts.

What is a Metal ? — Unfortunately it is not an easy thing
to give a satisfactory answer to this question.' We can give
examples of metals, such as iron, zinc, silver, calcium,
magnesium, etc.; but when we attempt to discover the
common properties of these substances we are somewhat at
a loss. In general, any element which has the power to
enter into an acid in the place of the hydrogen is called a
metal. With hydrogen and oxygen a metal forms a pro-
duct which has the power to neutralize acids; that is to
say, which has basic properties.

Names of Acids. — The termination ic is generally used in
naming acids, as is seen in the names hydrochloric, sul-
phuric, nitric, etc. If a second acid containing the same
elements exists and the proportion of oxygen contained in
it is smaller than in the acid the name of which ends in tc,
the second acid is given a name ending in ous. Thus,
chlorous acid, H0102, contains a smaller proportion of
oxygen than chloric acid, H0103.

When more than two acids containing the same elements
are known, prefixes are used to distinguish them. In the
series of chlorine acids already referred to (see page 87),
there is one acid which, so far as the proportion of oxygen
contained in it is concerned, stands below chlorous acid.
It is called A^ochlorous acid, the prefix hypo being derived
from a Greek word meaning under. Further, there is an
acid which contains a larger proportion of oxygen than
chloric acid. It is called perchloric acid, the Latin prefix
per meaning here very or fully. It will be seen that the
names of the acids vary with the proportion of oxygen con-
tained in them.

ACIDS— BASES— NEUTRALIZATION— SALTS. 93

Names of Bases. — As already stated, a base is a compound
of a metal with hydrogen and oxygen. Thus caustic soda
has the formula NaOH, caustic potash KOH, lime Ca02H2,
etc. They arc commonly known as hydroxides. To dis-
tinguish between the hydroxides of the different metals,
the names of the metals are put before the name hydroxide.
Thus, caustic soda, ISTaOH, is called sodium hydroxide ;
caustic potash, KOH, is called potassium "hydroxide ;
caustic lime, Ca02H2, is called calcium hydroxide, etc.
These compounds are called hydrates by some chemists.

Names of Salts.- — Every metal can form a salt with every
acid. The salts derived from a given acid receive a general
name, and this general name is qualified in each case by the
name of the metal contained in the salt. Thus, all the salts
derived from nitric acid are called nitrates ; all those de-
rived from chloric acid are called chlorates; those derived
from sulphuric acid are called sulphates. So too, further,
the salts of chlorous acid are called chlorites; those of
nitrous acid, nitrites; those of sulphurous acid, sulphites;
etc., etc. You will notice that the last syllable of the name
of the salt differs according to the name of the acid. If
the name of the acid ends in ie, the name of the salt ends
in ate. If the name of the acid ends in ous, the name of
the salt ends in ite. To distinguish between the different
salts of the same acid, the name of the metal contained in
it is put before the general name of the salt. Thus, the
potassium salt of nitric acid is called potassium nitrate,
the sodium salt is called sodium nitrate ; the calcium salt
of sulphuric acid is called calcium sulphate; the magnesium
salt of nitrous acid is magnesium nitrite ; the calcium salt
of hypochlorous acid is calcium hypochlorite, etc., etc.

[Give the name and formula of the potassium salt of

94 THE ELEMENTS OF CHEMISTRY.

perchloric acid. — Give the name and formula of the sodium
salt of hypochlorous acid. — Give the name and formula of
the sodium salt of nitric acid.]

Salts of Hydrochloric Acid. — If the salts of hydrochloric
acid were named in accordance with the principle just ex-
plained, they would be called TiydrocMorates. But these
salts are identical with the products formed by direct com-
bination of the metals with chlorine. Thus hydrochloric
acid and zinc act as represented in the equation

Zn + 2HC1 = ZnCl2 + 2H;

while zinc and chlorine act thus:

Zn + 201 = Zn012. .

In each case the same product, ZnCl2, is formed. But
these compounds of metals with chlorine are called chlo-
rides, as has already been explained. Hence the name
hydrochlorates is unnecessary.

Acid Properties and Oxygen. — The observation that oxy-
gen is generally present in acids led at one time to the be-
lief that it is a necessary part of these substances. Hence
the name oxygen, which means the acid-former, was given
to it. That oxygen is not essential to the existence of acid
properties is shown in the case of hydrochloric acid, and in
a few other similar cases. It must be said, however, that
the acid properties of substances are generally due to the
presence of oxygen. Some substances with basic properties
are converted into acids by causing them to combine with
more oxygen.

CARBON. 95

CHAPTER XII.
CARBON

Carbon Found in All Living Things. — Wood, flesh, and
other products of vegetable or animal life, when heated to
a sufficiently high temperature "blacken, and afterwards, if
they are heated in the air, they burn up, as we say. This
blackening is due to the fact that the substances all con-
tain carbon. When they are heated the other elements
are first driven off in various forms of combination, while
the carbon is the last to go. If they are heated in the air,
the carbon finally combines with oxygen to form a colorless
gas — it burns up.

Destructive Distillation. — The process of heating sub-
stances in closed vessels and collecting the products formed
is called destructive distillation. Among the most inter-
esting examples of destructive distillation are those of coal
and of wood. Coal is heated, as already stated under Am-
monia, for the purpose of making illuminating-gas. Wood
is heated for the purpose of making charcoal. Many in-
teresting and important substances are obtained in these
processes. Some of them will be taken up farther on.

Occurrence of Carbon. — From what has already been said
you will see that the principal form in which carbon occurs
in nature is in combination with other elements. It occurs
not only in all living things, but in their fossil remains, as

96 TEE ELEMENTS OF CHEMISTRY.

in coal. Coal-oil on petroleum, the formation of which was
in some way connected with the processes involved in the
formation of coal, consists of a large number of compounds
which contain only carbon and hydrogen. Most products
of plant-life contain the elements carbon, hydrogen, and
oxygen. Among the more common of these products are
sugar, starch, cellulose, etc. Most products of animal life
contain carbon, hydrogen, oxygen, and nitrogen. Among
them may be mentioned albumin, fibrin, casein, etc. Car-
bon occurs in the atmosphere in the form of carbon dioxide
or carbonic acid. It also occurs in the form of salts of car-
bonic acid, the carbonates, which are widely distributed,
forming some large mountain-ranges. Limestone, marble,
and chalk are calcium carbonate.

Forms of the Element Carbon. — Uncombined, the element
occurs pure in two very different forms in nature: (1) As
diamond; and. (2) as graphite or plumbago.

Diamond. — The celebrated diamond-beds are in the East
Indies, Borneo, Sumatra, Brazil, Australia, Mexico, and
the Cape of Good Hope. When found, diamonds are cov-
ered with an untransparent layer, which must be removed
before the beautiful properties appear. Diamond is the
hardest substance known. Heated to a high temperature
in oxygen, it burns up, forming only carbon dioxide.

Graphite. — Graphite, or plumbago, is found in nature in
large quantities. It can be prepared artificially by dissolv-
ing charcoal in molten iron. From this solution it is de-
posited as graphite on cooling. It has a grayish-black
color and a metallic lustre. It is quite soft, leaving a
leaden-gray mark on paper when drawn across it, and is
hence used in the manufacture of so-called lead pencils. It
is sometimes called black lead. Heated to a very high

CABBON. 97

temperature in the air, or in oxygen, it burns up, forming
only carbon dioxide.

Amorphous Carbon. — All forms of carbon which are not
diamond, nor graphite, are included under the name amor-
phous carton. This name means simply that it is not crys-
tallized.

How Charcoal is Made.— Charcoal is that form of carbon
which is made by the charring process. This consists sim-
ply in heating without a free supply of air. The substance
almost exclusively used in the manufacture of charcoal is
wood. Wood consists of a large number of substances,
nearly all of which are made up of the three elements car-
bon, hydrogen, and oxygen. When wood is burned in the
air the products are carbon dioxide and water. If the air
be prevented from coming freely in contact with the wood,
the hydrogen is given off partly as water and partly in the
form of volatile compounds containing carbon and oxygen.
The carbon, however, is mainly left behind as charcoal, as
there is not enough oxygen present to burn it.

A Charcoal-kiln. — This consists essentially of a pile of
wood so arranged as to leave spaces between the pieces.
The pile is then covered either with mason-work or some
rough material through which the air will not pass easily,
as, for example, a mixture of powdered charcoal, turf, and
earth. Small openings are left in the covering. The wood
is kindled and burns slowly. After a time the holes
through which the air gains access to the wood are closed
up, and the process stops. Charcoal, which is impure
amorphous carbon, is left behind.

Properties of Charcoal. — Ordinary charcoal is a black,
comparatively soft substance. It burns in the air, though
7

98 THE ELEMENTS OF CHEMISTRY.

not easily, unless the gases which are formed are constantly
removed and fresh air is supplied, as by blowing with a
bellows. It burns readily in oxygen, as we have seen (Ex-
periment 24). The product of the combustion in oxygen
and in air, when there is no lack of oxygen, is carbon di-
oxide, C02. In the air when the draught is bad, another
compound of carbon and oxygen, carbon monoxide, CO, is
formed.

Coke. — This is a form of amorphous carbon which is
made by heating ordinary gas-coal without access of air, as
is done on a large scale in the manufacture of illuminating-
gas. Coke bears to coal about the same relation that char-
coal bears to wood.

Lamp-black is a very finely divided form of charcoal
which is deposited on cool objects placed in the flames of
burning oils. Most flames used for illuminating purposes
give a black deposit of soot on objects placed in them.
This soot is largely made up of fine particles of carbon.
It is used in the manufacture of printer's ink. Carbon is
acted upon directly by very few substances, and is insolu-
ble, so that it is impossible to destroy the color of printer's
ink without destroying the material upon which it is im-
pressed.

Bone-black, or Animal Charcoal, is a form of amorphous
carbon which is made by charring bones and other ani-
mal substances. Unless it is treated with an acid it con-
tains the incombustible substances which form a part of
bones.

Charcoal-filters. — Bone-black and wood-charcoal are very
porous and have the power to absorb gases. When placed
in air containing bad-smelling gases, these are absorbed

CARBON. 99

and the air thus purified. When water which contains
disagreeable substances is treated with charcoal, these are
wholly or partly absorbed and the water improved. Char-
coal-filters are therefore extensively used. A charcoal-fil-
ter to be of value should be of good size, and from time to
time the charcoal should be taken out and renewed. The
small filters which are screwed into faucets are of little
value, as the charcoal soon becomes charged with any ob-
jectionable matter which may be present in the water.

Bone-black Filters. — Some coloring matters are removed
from liquids by passing the liquids through bone-black fil-
ters. On the large scale, this fact is taken advantage of in
the refining of sugar. The solution of sugar first obtained
from the cane or beet is strongly colored; and if it were
evaporated, the sugar deposited from it would be dark-
colored. If, however, the solution be first passed through
bone-black filters, the color is removed.

Experiment 68. — Make a filter of bone-black by fitting a paper
filter into a funnel 12 to 15 mm. (5 to 6 inches) in diameter at its
mouth. Half fill this with bone-black. Pour a dilute solution
of indigo* through the filter. If the conditions are right the so-
lution will pass through colorless. — Do the same thing with a di-
lute solution of litmus. — If the color is not completely removed
by one filtering, filter the solutions again. — The color may also be
removed from solutions by putting some bone-black into them
and boiling for a time. Try this with half a litre each of the lit-
mus and indigo solutions used in the first part of the experiment.
Use about 4 to 5 grams bone-black in each case. Shake the solu-
tions frequently while heating.

Charring Prevents Decay. — Charcoal does not decay in
the air or under water nearly as readily as wood. That is

* Prepared by treating powdered indigo for some time with warm
Concentrated sulphuric acid and diluting with much water.

100 THE ELEMENTS OF CHEMISTRY.

another way of stating the chemical fact that the substan-
ces of which wood is made up are more susceptible to the
action of other chemical substances than charcoal is. We
have one illustration of this in the relative ease with which
charcoal and wood burn in the air. Piles which are driven
below the surface of water are charred to protect them
from the action of those substances which cause decay.

Coal. — Under this head are included a great many kinds
of impure amorphous carbon which occur ready-formed in
nature. Ordinarily coals are divided into hard and soft
coals, or anthracite and bituminous coals. Then there are
substances more closely related to wood and therefore
called lignite, and those which represent a very early stage
in the process of coal-formation, viz., peat.

Formation of Coal. — A close examination of all these
varieties has shown that they have been formed by the
gradual decomposition of vegetable material where there
was not free access of air. The process has been going on
for ages. Sometimes the substances have been subjected to
great pressure, as can be seen from the position in which
they occur in the earth.

Destructive Distillation of Coal. — All forms of coal con-
tain other substances besides carbon. The soft coals are
particularly rich in other substances. When heated they
give off a mixture of gases and vapors of volatile liquids.
The gases are, foj the most part, useful for illuminating
purposes. The liquids form a black, tarry mass known as
coal-tar, from which are obtained many valuable compounds
of carbon. The gases are passed through water for the
purpose of removing certain impurities. This water ab-
sorbs ammonia and forms the ammoniacal liquor of the
gas-works,

CARBOK 101

Diamond, Graphite, and Charcoal Different Forms of the
Element Carbon. — An element, as you have learned, is a
form of matter which cannot be decomposed into simpler
substances by any means now known to chemists. From
hydrogen we can get nothing but hydrogen, except by
bringing it together with some other element; from nitro-
gen we can get nothing but nitrogen, etc. In the case of
carbon, however, it is possible for the element to appear in
three forms, which differ markedly from one another.
That they are the same substance, chemically speaking,
can be proved by a sijnple experiment. If we were to burn
the same weight of diamond, of graphite, and of charcoal,
and collect and weigh the carbon dioxide formed in each
case, we should find that the quantity of carbon dioxide
formed is the same in each case. Further, knowing the
composition of carbon dioxide, we know how much carbon
is contained in a given weight of the gas. Calculating the
quantity of carbon contained in the carbon dioxide ob
tained in burning a piece of diamond, we should find that
it is exactly equal to the weight of the diamond; and the
same thing is true of graphite and charcoal.

Problem. — How much carbon dioxide, C02, should be ob-
tained by burning 0. 5 gram diamond ? The combining weight of
carbon is 12.

Common Properties of the Different Forms of Carbon. —

Notwithstanding the marked differences in their appear-
ance the different forms of carbon have some properties in
common. They are insoluble in all known liquids. They
are tasteless, inodorous, and infusible. When heated with-
out access of air, they remain unchanged unless the tem-
perature is very high.

Alloteopism. — That one and the same substance can ap-

102 THE ELEMENTS OF CHEMISTBY.

pear in markedly different forms under different conditions
is seen in the case of water. Hail and snow would hardly
be suspected of being the same substance by one not quite
familiar with them. The difference in this case, as in that
of carbon, is believed to be due to the way in which the
small particles of which the substances are made up are
arranged. If we had a number of small pieces of wood all
of the same size and shape, say cubes, and should carefully
arrange them in some regular way, we might easily make
a comparatively compact mass of them., and the mass
would have a regular form. We might, further, arrange
them in some second way with regularity. And we might
simply throw the pieces together in a jumble. These three
kinds of arrangement would represent, in a rough way, the
difference between the three forms of carbon. Each pile
would be made of wood, but in outward appearance they
would differ from one another. In a similar way oxygen
and ozone differ from each other. The power which some
elements have of existing in different conditions is called
allotropism.

Chemical Conduct of Carbon. — At ordinary tempera-
tures carbon is an inactive element. If it be left in con-
tact with any one of the elements thus far considered —
viz., hydrogen, oxygen, chlorine, and nitrogen — no change
takes place. At higher temperatures, however, it readily
combines with other elements, especially oxygen. It com-
bines with oxygen either directly, as when it burns in the
air or oxygen; or it abstracts oxygen from some of the ox-
ides.

Direct Combination of Carbon with Oxygen. — This has
been already shown in Experiment 24, and is familiar to
every one in charcoal-fires. That carbon dioxide is tlie

CARBON.

103

product formed may be shown by passing the gas into lime-
water, when insoluble calcium carbonate will be thrown
down.

Experiment 69. — Put a small piece of charcoal in a piece of
hard glass tube. Pass oxygen through the tube, at the same
time heating it. Pass the gases into clear lime-water. Arrange
the apparatus as shown in Fig. 31. A is a bottle containing

Fig. 31.

oxygen; B is the hard glass tube containing the charcoal; C is
the cylinder with clear lime-water. The reason why lime-water
is used is simply that an insoluble compound is formed, and this
can be seen, and it can be separated from the liquid and exam-
ined. The reaction which takes place is represented thus:

Ca02H2 + C02 = CaC03 + H20.
Lime and «£g£ give ^*™ and water,
(insoluble)

No other common gas acts in this way with lime-water. Hence,
when, under ordinary circumstances, a gas is passed into lime-
water and an insoluble substance is formed, we may conclude that
the gas is carbon dioxide.

Carbon Abstracts Oxygen from Oxides.

lustrated by the following experiments ;

-This may be il-

104

TEE ELEMENTS OF CHEMISTRY.

Fig. 32.

Experiment 70.— Mix together 2 or 3 grams powdered coppre
oxide, CuO, and about one tenth its weight of powdered charcoal;

heat in a tube to which is fitted an
outlet tube, as shown in Fig. 32.
Pass the gas which is given off into
clear lime-water contained in a test-
tube.— Is it carbon dioxide ? What
evidence have you that oxygen has
been extracted from the copper ox-
ide ? What is the appearance of the
substance left in the tube ? Does it
suggest the metal copper ? Treat a
little with strong nitric acid. What
should take place if the substance is
metallic copper? (See Experiment
56.) What does take place? The
reaction between the charcoal and the copper oxide is represented
thus:

2CuO + C = 2Cu + C02.

Experiment 71.— Perform a similar experiment with a little
white arsenic in a small glass tube closed at one end. Take
about equal parts of charcoal and arsenic. White arsenic is a
compound of the element arsenic and oxygen, As203. The re-
action which takes place when it is heated with charcoal is repre-
sented thus :

2As203 + 30 = 4As + 3C02.

The element arsenic is volatile, and is hence driven out of the
bottom of the tube and deposited on the sides of the tube above
the mixture in the form of a mirror with a metallic lustre.

Use of Carbon (Charcoal) as a Reducing Agent.— As has

already been explained, the abstraction of oxygen from a
compound is known as reduction. Hence carbon is called
a reducing agent. It is extensively used for the purpose of
extracting metals from their ores, which are the forms in
which they occur in nature. Thus, iron does not occur in
nature as iron, but in combination with other elements,
particularly oxygen. In order to get the metal the org

CABBOF. 105

must be reduced,, or, in other words, the oxygen must be
extracted. This is invariably accomplished by heating it
with some form of carbon, either charcoal or coke.

[What other element which you have already studied
acts as a reducing agent ? Give an example of its reducing
power.]

106 THE ELEMENTS OF CHEMISTRY.

OHAPTEE XIII.

COMPOUNDS OF CARBON WITH HYDROGEN;
OXYGEN, AND WITH NITROGEN.

Compounds of Carbon and Hydrogen. — In the laboratory
it is not a simple matter to effect combination between car-
bon and hydrogen except in a few simple cases. In nature
processes are in operation which give rise to the formation
of a. large number of compounds containing these elements;
and, further, in the manufacture of illuminating-gas from
coal the conditions are such as to cause the combination of
carbon and hydrogen, several interesting compounds being
thus formed. There are no other two elements which
combine with each other in as many different proportions
as carbon and hydrogen. The compounds thus formed are
known as hydrocarbons. The number of hydrocarbons
known is very great, being somewhere between one and two
hundred. Fortunately, investigation has shown that quite
simple relations exist between these compounds; and hence,
though the number is large, the study is not as difficult as
might be expected.

Petroleum is an oily liquid found in many places in the
earth in large quantity, particularly in Pennsylvania and
the Caucasus. In the earth it contains both gases and liq-
uids. When it is brought into the air, the pressure being
removed, the gases are given off . There are several gas-
eous hydrocarbons given off, and a large number of liquids
left behind.

COMPOUNDS OF CARBON 107

Refining Petroleum. — The vapors from petroleum when
mixed with air are explosive, and the thicker liquids clog
the lamps and wicks. Therefore these must be removed
before the oil is fit for household use. This is done by (1)
distilling, (2) washing with sulphuric acid, (3) washing
with alkali, and (4) washing with water. The product thus
prepared is called kerosene.

In refining petroleum a numbei of products are obtained
which cannot be used in lamps. Those which are lighter
than kerosene, that is to say those which boil at a lower
temperature, are known as gasoline, naphtha, lenzine, etc.
From the heavier portions, or those which boil at higher
temperatures than kerosene, paraffin is made. Each ovf
these substances is a mixture of several chemical com-
pounds.

Hydrocarbons contained in Petroleum. — The simplest
hydrocarbon contained in petroleum is methane, or marsh-
gas, CH4; the next has the composition C2H6, the next
C3H8, etc. It will be seen that these compounds bear a
simple relation to one another, as far as composition is
concerned. They are the first members of a series the
names and symbols of the first eight members of which are
given below:

CH4, Methane, or Marsh-gas;

02H6, Ethane;

C3H8, Propane;

04H10, Butane;

C5H12, Pentane;

C6H14, Hexane;

C7H16, Heptane;

08H18, Octane.

108 THE ELEMENTS OF CHEMISTRY.

Homology.— -The first member of the series differs from
the second by CH2; there is also this same difference, in
general, between any two consecutive members of the series,
This relation is known as homology, and such a series as an
homologous series. Carbon is distinguished from all other
elements by its power to form homologous series.

The Ethylene Series of Hydrocarbons. — Besides the series
above mentioned which is known as the marsh-gas series,
there are other homologous series of hydrocarbons. There
is one beginning with ethylene, C2H4, examples of which
are

Ethylene, C2H4;
Propylene, C3H6;
Butylene, C4H8.

The Acetylene Series. — There is a series beginning with
acetylene, examples of which are

Acetylene, C2H2;
Allylene, C3H4.

The Benzene Series. — Another series begins with benzene,
C6H6. Some of the members of this series are

Benzene, 06H6;
Toluene, 07H8;
Xylene, 08H10.

Marsh-gas, Methane, Fire-damp, CH4. — Marsh-gas is
found in nature in petroleum, and is given off when the
oil is taken out of the earth. It is formed, as the name
implies, in marshes, as the product of a reducing process.
Vegetable matter is composed of carbon, hydrogen, and
oxygen. When it undergoes decomposition in the air in a

COMPOUNDS OF CABBON. 109

free supply of oxygen, the final products are carbon dioxide
and water. When the decomposition takes place without
access of oxygen, as under water, marsh-gas, which is a re-
duction product, is formed. It bears to carbon much the
same relation that ammonia bears to nitrogen.

Occurrence of Marsh-gas in Coal-mines. — Marsh-gas is
met with in coal-mines, and is known to the miners as fire-
damp. Mixed with air it is one of the causes of the terrible
explosions which occur in coal-mines.

Preparation of Marsh- gas. — Marsh-gas is most readily
prepared In the laboratory by heating sodium acetate with
caustic potash and quicklime.

Experiment 72. — Mix 5 grains dry sodium acetate, 5 grams
potassium hydroxide, and 7-J grams quicklime. Heat in a retort.
Collect over water as in making nitrous oxide. Does the gas
burn ? Does it give light in burning ?

Properties of Marsh-gas. — Marsh-gas is a colorless, trans-
parent, tasteless, inodorous gas slightly soluble in water.
It burns, forming carbon dioxide and water. When mixed
with air, the mixture explodes if a flame or spark comes in
contact with it.

Ethylene, Olefiant Gas, 02H4.— This hydrocarbon is formed
by heating a mixture of ordinary alcohol and concentrated
sulphuric acid. It is a colorless gas which can be con-
densed to a liquid. It burns with a luminous flame.

Acetylene, C2H2. — Acetylene is formed when a current of
hydrogen is passed between carbon poles which are incan-
descent in consequence of the passage of a powerful elec-
tric current. In this case carbon and hydrogen combine
directly. It is formed also when the flame of an ordinary
laboratory burner (Bunsen burner) ci strikes back, " or burns
at the base without a free supply of air. Its odor is un-
pleasant,, It burns with a luminous, smoky flame.

110 THE ELEMENTS OF CHEMISTRY.

The Manufacture of Illuminating-gas. — The gas which
is used for lighting buildings is generally made from coal.
For this purpose, as has been stated, the coal is heated in
closed vessels. The products which are formed are first
passed through a series of tubes which are kept cool. In
these a thick black liquid, known as coal-tar , collects.
Then the gaseous products are passed through water which i
takes up ammonia. The gases which remain are treated
with two or three other substances to remove impurities,
and are then collected in large vessels called gasometers.
One ton of gas-coal yields an average of 10,000 cubic feet
of gas.

Coal-tar. — Coal-tar contains a very large number of
compounds, some of which are obtained from it by distil-
lation. The first products which pass over contain the
hydrocarbons of the benzene series, of which benzene itself
is the principal one.

Carbon Dioxide, C02.— The principal compound of carbon
and oxygen is carbon dioxide, C02, commonly called car-
bonic acid.

Occurrence of Carbon Dioxide.— Under the head of The
Atmosphere it was stated that this gas is always present in
the air. It issues from the earth in many places, particu-
larly in the neighborhood of volcanoes. Many mineral
waters contain it in considerable quantity, as the waters of
Pyrmont, Selters, and the Geyser Spring at Saratoga. In
small quantity it is present in all natural waters. In com-
bination with bases it occurs in enormous quantities, par-
ticularly in the form of calcium carbonate, CaC03, varie-
ties of which are ordinary limestone, chalk, marble, and
calc-spar.

Natural Formation of Carbon Dioxide. — Carbon dioxide

COMPOUNDS OF CARBON.

Ill

is constantly formed in many natural processes. Thus, all
animals that breathe in the air give off carbon dioxide from
their lungs.

Experiment 73. — Blow through, some lime-water by means of
an apparatus arranged as shown in Fig 33. What evidence have
you that your lungs give off car-
bon dioxide ?

It has already been shown
that carbon dioxide is formed
in the combustion of charcoal
and wood. In a similar way
it can be shown that the gas
is formed whenever any of our
ordinary combustible materials
are burned. From our fires
as from our lungs, and from fig. 33.

the lungs of all animals, then, carbon dioxide is constantly
given off. Further, the natural processes of decay of
both vegetable and animal matter tend to convert the
carbon of this matter into carbon dioxide, and this is
then spread through the air. The process of alcoholic
fermentation, and some other like processes, also give rise to
the formation of carbon dioxide. In all fruit-juices there
is contained sugar. When the fruits ripen, fall off, and
"decay, the sugar is changed to alcohol and carbon dioxide.

Preparation of Carbpn Dioxide. — The easiest way to get
carbon dioxide is to add an acid to a carbonate. When-
ever any acid is added to any carbonate there is an evolu-
tion of gas.

Experiment 74. — In different test-tubes containing a little
sodium carbonate add dilute hydrochloric, sulphuric, nitric, and
acetic acids. — What takes place? Is a gas given off? Pass it
through lime-water. Is it carbon dioxide ? — Perform the same
experiment with small pieces of marble. What gas is given off $

112

THE ELEMENTS OF CHEMISTRY.

To prepare carbon dioxide in the laboratory, calcium
carbonate in the form of marble, or limestone, and hydro-
chloric acid are commonly used. The reaction is repre-
sented thus :

CaC03 + 2H01 = 0aCl2 + C02 + H20o

Calcium
carbonate.

[What is the substance Ca012 ?]

Experiment 75. — Arrange an apparatus as shown in Fig. 34.
In the flask put some pieces of marble, and pour ordinary hydro-
chloric acid on it. Collect the gas by displace-
ment of air, placing the vessel with the mouth up-
ward. Fill several cylinders or bottles with the
gas. — Into one introduce a lighted candle, and
afterwards a burning stick. What takes place ?
Into another put a live mouse. What takes place ?
With another proceed as if pouring water from it.
Pour the invisible gas upon the flame of a burning
candle. Pour some of the gas from one vessel
to another, and show that it has been trans-
ferred. Balance a beaker on a good-sized scales,
and pour carbon dioxide into it. If the balance
is at all sensitive, the pan in which the beaker is
Fig. 34. placed will go down.

Properties of Carbon Dioxide. — From the observations
you have just made you have learned that carbon dioxide
is a colorless gas at the ordinary temperature ; that it is in-
combustible and does not support combustion; and that it
is heavier than the air. When subjected to a low temper-
ature and high pressure it is converted into a liquid, and
this can further be changed to a solid. It has a slightly
acid taste and smell.

Why Carbon Dioxide does not Burn. — It does not burn
for the same reason that water does not ; because it already

COMPOUNDS OF CABBON 113

holds in combination all the oxygen it has the power to
combine with. Before it can burn again it must first be
decomposed.

Carbon can do Chemical Work. — Carbon has the power
to combine with oxygen, and in so doing a definite quan-
tity of heat is given off. A pound of carbon represents a
definite quantity of chemical energy, which we can get,
first, in the form of heat, and then convert into other forms,
as electricity, motion, etc. After the pound of carbon has
been burned, the product no longer represents the energy
the carbon did. Similarly, a body of water elevated ten
or fifteen feet represents a certain quantity of energy which
can be obtained by allowing the water to fall upon the
paddles of a water-wheel connected with the machinery of
a mill. After the water has fallen, however, it no longer
has the power to do work, or it has no energy. In order
that it may again do work it must again be lifted up.

Soda-water. — Carbon dioxide dissolves in water, one
volume of water dissolving about its own volume of the gas
at the ordinary temperature. When the pressure is in-
creased the water dissolves more gas; and when the pres-
sure is removed the gas again escapes. The so-called
" soda-water" is simply water charged with carbon dioxide
under pressure. The escape of the gas, when the water is
drawn, is familiar to every one. The carbon dioxide used
in charging the water is usually made from a sodium salt
of carbonic acid known as "bicarbonate of soda."

Breathing. — It was stated above that carbon dioxide is
given off from the lungs as it is from a fire, and the fact
was shown by means of a simple experiment. It is a waste
product of the processes going on in the animal body.
Just as it cannot support combustion, so animals cannot
8

114 THE ELEMENTS OF CHEMISTRY.

,

breathe in it. It is not poisonous any more than water is;
but it cannot supply the oxygen which is needed for breath-
ing purposes. In it animals die of suffocation, as they do
in water. Any considerable increase in the quantity of
carbon dioxide in the air above that which is generally
present is objectionable, because it decreases the propor-
tion of oxygen in the air which is breathed. If pure car-
bon dioxide be introduced into the air it has been shown
that as much as 5 per cent may be present without causing
injury to those who breathe it.

Air in Badly Ventilated Rooms. — In a badly ventilated
room in which a number of people are collected and lights
are burning, it is well known that in a short time the air
becomes foul, and bad effects, such as headache, drowsi-
ness, etc., are felt by those in the room. These effects are
caused, not by the carbon dioxide, but by other waste
products which are given off from the lungs in the process
of breathing. - The gases given off from the lungs consist
of nitrogen, oxygen, carbon dioxide, and water-vapor.
Besides these, however, there are many substances in a fine
state of division which contain carbon, and are in a state
of decomposition. These are poisonous, and are the chief
cause of the bad effects experienced in breathing air which
has become contaminated by the exhalations from the
lungs.

Carbon Dioxide in Old Wells. — As carbon dioxide is
formed in the earth wherever an acid solution comes in
contact with a carbonate, the gas is frequently given off
from fissures in the earth. It is hence not infrequently
found in old wells which have not been in use for some
time, and deaths have been caused by descending these
wells for the purpose of repairing them. It is a good plan

COMPOUNDS OF CARBON 115

to let down a lighted candle into such a well before ventur-
ing to go down. If the candle burns, the air can be
breathed without danger.

Choke-damp. — Carbon dioxide is also frequently met
with in mines, and is called choke-damp by the miners.
The miners know that after an explosion caused by fire-
damp there is danger of death from choke-damp. The
reason is simple. "When fire-damp, or marsh-gas, explodes
with air the carbon is converted into choke-damp, or car-
bon dioxide, and the hydrogen into water.

Carbon Dioxide the Food of Plants. — Plants live largely
on the carbon dioxide contained in the air. They have the
power with the aid of the sun's light to decompose the
gas, and they then build up the complex compounds of car-
bon which form their tissues, using for this purpose the
carbon of the carbon dioxide which they have decomposed.

Plants the Food of Animals. — Animals eat either the
products of plant-life or other animals which get their
food from the vegetable kingdom. The food of animals
comes, then, either directly or indirectly from plants. The
food taken into the animal body is partly changed into
other substances which form the structure of the animal;
and partly it is oxidized, thus serving to keep the tempera-
ture of the body up to the necessary point. That part of
the food which suffers oxidation in the body acts the same
as fuel in a stove. It is burned up, producing heat, the
carbon being converted into carbon dioxide which is given
off from the lungs.

Carbon Dioxide Returns to the Air. — From fires and
living things carbon dioxide is returned to the air, where
it again serves as food for plants. When the life-process
stops in the animal or plant, decomposition begins; and

116 THE ELEMENTS OF CHEMISTBY.

the final result of this,, under ordinary circumstances, i
the conversion of the carbon into dioxide.

No Life Without the Sun.— Every living thing is depen-
dent upon the decomposition of carbon dioxide by plants
and this decomposition cannot be effected without the aid
of the sun. If the sun should stop shining, soon all life
would cease. As the heat of the sun acting upon the great
bodies of water and on the air gives rise to the movements
of water which are essential to the existence of the world
as it is, so the action of the sun^s rays on carbon dioxide,
in the presence of the delicate and inexplicable mechanism
of the leaf of the plant, gives rise to those changes in the
forms of combination of the element carbon which accom-
pany the wonderful process of life.

Carbonic Acid. — A solution of carbonic acid in water has
a slightly acid reaction. The solution will act upon basic
solutions and form salts. The composition of the sodium
salt formed in this way is Na2C03 ; that of the potassium
salt K2C03, etc. These salts are plainly derived from an
acid, H2003, which is carbonic acid. It is probable that
the acid is contained in the solution. of carbon dioxide in
water. It is, however, so unstable that it breaks up into
carbon 'dioxide and water :

H2C0s = C02 + Ha0.

The Carbonates. — When carbon dioxide acts upon a base
it forms a salt. Thus, when potassium hydroxide or cal-
cium hydroxide is used, the action which takes place is
represented thus :

2KOH + CO, - K2003 + H20 ;
CaO1H, + CO1 = CaCOi + H,0,

COMPOUNDS OF CARBON. Ill

Experiment 76. — Pass carbon dioxide into a solution of caustic
potash until it will absorb no more. Add acid to some of the
solution thus obtained, and convince yourself that the gas given
off is carbon dioxide. Write the equations separating the re-
actions which take place on passing the carbon dioxide into the
caustic-potash solution, and on adding an acid to the solution.
What evidence have you that the gas given off is carbon dioxide ?

Experiment 77. — Pass carbon dioxide into 50 to 100 cc. clear
lime-water. Filter off the white insoluble substance. Try the
action of a little acid on it. What evidence have you that it is
calcium carbonate ? How could you easily distinguish between
lime-water and a solution of caustic potash ?

Calcium Carbonate Dissolves in Water containing Carbon
Dioxide. — If you continue to pass carbon dioxide into lime-
water after the calcium carbonate has been formed, the
carbonate dissolves, and the solution finally becomes clear.
If this solution be heated, the carbon dioxide is driven off
and the calcium carbonate is again thrown down.

Experiment 78. — Pass carbon dioxide first through a little
water to wash it, and then into 50 to 100 cc. clear lime-water.
After the solution has become clear, heat it.

Hard Water. — Natural waters which flow over limestone
take up more or less calcium carbonate by virtue of the
carbon dioxide which they absorb from the air. Such
waters, which are called " hard waters/' are in the condi-
tion of the solution of calcium carbonate above referred to.
When heated, the calcium carbonate is deposited. This
is frequently noticed in the deposits in boilers and other
vessels in which water is boiled. This kind of hardness is
called "temporary hardness/' to distinguish it from "per-
manent hardness" which is not affected by boiling.

Carbon Monoxide, CO. — This compound is formed when a
substance containing carbon is burned in an insufficient
supply of air, — as, for example, when the draught in a

118 THE ELEMENTS OF CHEMISTRY.

furnace is not strong enough to remove the products of
combustion and supply fresh air. It can also be made by
extracting oxygen from carbon dioxide. It is only neces-
sary to pass the dioxide over heated carbon, when the reac-
tion which is represented in the following equation takes
place :

CO, + 0 = 200.

Formation of Carbon Monoxide in Coal-fires. — The for-
mation of carbon monoxide can be well observed in a hard-
coal fixe in an open grate. The air has free access to the
coal, and at the surface complete oxidation takes place.
But that part of the carbon dioxide which is formed at the
lower part of the grate is drawn up through the heated
coal and is partly reduced to carbon monoxide. When the
monoxide escapes from the upper part of the grate it
again combines with oxygen, or burns, causing the char
acteristic blue flame always noticed above a mass of burn-
ing hard coal.

Carbon Monoxide contained in Water-gas. — Water-gas,
as has been stated under Hydrogen, is made by passing
water- vapor over highly heated coal, when this reaction
takes place :

0 + H20 = 00 + 2H.

The gas obtained is therefore a mixture hi carbon mon-
oxide and hydrogen. Before use it is enriched by the ad-
dition of hydrocarbons from petroleum. As carbon mon-
oxide is poisonous, laws have been passed in some States
prohibiting the use of water-gas.

Preparation of Carbon Monoxide. — Carbon monoxide is
most easily made by heating oxalic acid, C2H20^, with

COMPOUNDS OF CABBON. 119

sulphuric acid. The change which takes place is repre-
sented thus :

CaH204 = CO, + CO + H20.

Both carbon dioxide and monoxide are formed. Both
are gases. In order to separate them the mixture is
passed through a solution of caustic soda, which takes up
the carbon dioxide [forming what ?] and allows the mon-
oxide to pass.

Experiment 79. — Put ten grams crystallized oxalic acid and
50-60 grams concentrated sulphuric acid in an appropriate-sized
flask. Connect with two Wolffs flasks containing caustic-soda
solution. Heat the contents of the flask gently. Collect some of
the gas over water. Set fire to the same, and notice the charac-
teristic blue flame.

Properties of Carbon Monoxide. — It is a colorless, taste-
less, inodorous gas, insoluble in water. It burns with a
pale blue flame, forming carbon dioxide. It is exceedingly
poisonous when inhaled. Hence it is very important that
it should not be allowed to escape into rooms occupied by
human beings,

Danger of Coal-stoves. — We not unfrequently hear of
deaths caused by the gases from coal-stoves. The most
dangerous gas given off from coal-stoves is probably carbon
monoxide. A pan of smouldering charcoal gives off this
gas, and the poisonous character of the gas is well known.

Carbon Monoxide a Reducing Agent. — At high temper-
atures carbon monoxide has a very strong attraction for
oxygen, and is hence a good reducing agent. In the re-
duction of iron from its ores the carbon monoxide formed
in the blast-furnace plays an important part.

Experiment 80. — Pass carbon monoxide over some heated
copper oxide contained in a hard glass tube. Is the oxide re-

120 THE ELEMENTS OF CHEMISTRY.

duced ? How do you know ? Is carbon dioxide formed ? What
evidence have you ? Was the carbon monoxide free of carbon
dioxide ? If not, what evidence have you that carbon dioxide is
formed in this experiment ?

Illumination. — In all ordinary forms of illumination we
are dependent upon flames for the light. Whether we use
illuminating-gas, a lamp, or a candle, the light comes from
a flame. In the first case, the gas is burned directly ; in
the case of the lamp, the oil is first drawn up the wick,
then converted into a gas, and this burns ; while, finally,
in the case of the candle, the solid material of the candle
is first melted, then drawn up the wick, converted into gas,
and the gas burns, forming the flame. In each case we
have, then, a burning gas, and this burning gas we call a
flame.

When Burning Gases are Cooled Down they are Extin-
guished.— You have already learned that substances need
to be raised to the kindling temperature, before they will
burn. This statement is as true of gases as of other sub-
stances. When a current of hydrogen is allowed to escape %
into the air, or into oxygen, no action takes place unless it
be heated up to the burning temperature, when it takes
fire and continues to burn. If the gas be cooled down ever
so slightly, it is extinguished.

Experiment 81. — Light a Bunsen burner. Bring down upon
the flame a piece of brass or iron wire gauze. There is no flame
above the gauze. That the gas passes through unburned can be
shown by applying a light just above the outlet of the burner and
above the gau*e. The gas will take fire and burn. By simply
passing through the thin wire gauze, then, the gas is cooled down
below its burning temperature. Turn on a Bunsen burner. Do
not light the gas. Hold a piece of wrire gauze about one and a
half to two inches above the outlet. Apply a lighted match
above the gauze, when the gas will burn above the gauze, but not
below it.

COMPOUNDS OF CABBOK

121

The Safety-lamp. — The facts illustrated in the last experi-
ments are utilized in the miner's safety-lamp. One of the
dangers which the miner has to encounter
is the occurrence of fire-damp, or meth-
ane, CH4, which with air forms an explo-
sive mixture. The explosion can only be
brought about by contact of a flame with
the mixture. In order to avoid the con-
tact, the flame of the safety-lamp is sur-
rounded by wire gauze, as shown in Fig.
35. When a lamp of this kind is brought
into a mixture of marsh-gas and air, it, of
course, passes through the wire gauze and
comes in contact with the flame. A small
explosion occurs inside the gauze, but the
flame inside cannot pass through. Hence
no serious explosion takes place. The
flickering of the flame, and the occurrence
of small explosions inside the gauze, fur-
nish the miner with the information that
he is in danger.

Causes of the Luminosity of Flames. — There are several
causes which make flames give light. One is the presence
of solid substances in the flame. If a piece of platinum
wire be put in a hydrogen flame which gives practically no
light the flame becomes luminous. This fact has also been
shown by introducing a piece of lime into the hot, non-
luminous flame of the oxyhydrogen blow-pipe. A similar
cause makes ordinary gas-flames luminous. There are
always present in these flames particles of unburned carbon,
as is shown by putting a solid substance into the flames,
when a layer of soot, which consists mainly of finely divided

Fig. 35.

122 THE ELEMENTS OF CHEMISTRY.

carbon, is deposited on it. Again, the denser the gas the
more light it gives. A candle on the top of a high moun-
tain, as Mont Blanc, on which the experiment was per-
formed, gives less light than the same candle does at the
level of the sea.

Cyanogen, C2lSr2. — Carbon does not combine with nitro-
gen under ordinary circumstances. If, however, they are
brought together at very high temperatures in the pres-
ence of metals, they combine to form compounds known
as cyanides. When refuse animal substances, such as
blood, horns, claws, hair, wool, etc., are heated togeth-
er with potassium carbonate and iron, a substance known
as potassium ferrocy article, or yellow prussiate of potash,
K4Fe06N6 + 3H20, is formed. When this is simply heated
it decomposes, yielding potassium cyanide, KCN". From
the potassium compound it is not difficult to make mercury
cyanide, Hg(CN)2. By heating mercury cyanide it breaks
up, yielding mercury and cyanogen gas:

Hg(CF)2 = Hg + C2N2.

[What analogy is there between this reaction and that
which takes place when mercury oxide is heated?]

Properties. — Cyanogen is a colorless gas, easily soluble in
water and alcohol. It is extremely poisonous.

Hydrocyanic Acid, Prussic Acid, HON. — This acid occurs
in nature in combination with other substances, — in bitter
almonds, the leaves of cherry, laurel, etc. It is prepared
from potassium cyanide, just as hydrochloric acid is pre-
pared from sodium chloride. The reaction is:

2KCN + HaS04 = K2S04 + 2HCK

COMPOUNDS OF CARBON 123

Properties — Hydrocyanic acid is a volatile liquid. It
has a very characteristic odor resembling that of bitter
almonds. It is extremely poisonous. It dissolves in water
in all proportions, and it is such a solution which is known
as prussic acid.

Other Compounds of Carbon. — That part of Chemistry
which has to do with the compounds of carbon is commonly
called Organic Chemistry. It is more convenient to con-
sider this subject after the chemistry of the other common
elements has been studied. The last part of this book will
treat of some of the more common and better known com-
pounds of carbon.

124 THE ELEMENTS OF CHEMISTRY.

CHAPTER XIV.

ATOMIC THEORY — ATOMIC WEIGHTS — MOLECULAR
WEIGHTS — VALENCE — CLASSIFICATION OF THE
ELEMENTS.

The Laws of Chemical Action. — You have learned that
there are two laws always governing chemical combination.
These are the laws of definite and multiple proportions.
These laws are simply statements which sum up what has
been found to be true in ail cases examined. They are
statements of facts discovered by actual experiment.

We may Know a Fact without Knowing its Cause. — It is
one thing to know a general fact, and quite another to
know the cause of the fact. We know that all bodies are
attracted by the earth, and that they fall when thrown into
the air. But we do not know why this is so. So, too,
though we know that substances combine according to the
laws of definite and multiple proportions, it does not neces-
sarily follow that we know why they combine according to
these laws.

Hypothesis and Theory. — When a law has been discovered
by careful study of the facts, the next thing to be done is
to imagine d cause. We try to imagine a condition of
things which, if it existed, would lead to the results discov-
ered. If we succeed in imagining such a condition of
things we suggest an hypothesis. If, now, we test this hy-
pothesis in every way that suggests itself, and find that all
facts discovered are in accordance with it, we then call it a

ATOMIC THEORY-VALENCE. 125

theory. An hypothesis is a guess in regard to the cause oi
certain phenomena. A theory is an hypothesis which has
been thoroughly tested, and which is applicable to a large
number of related phenomena.*

The Atomic Theory. — The atomic theory was suggested
to account for the laws of definite and multiple proportions.
The theory is simply this:

That all kinds of matter are made up of indivisible par-
ticles called atoms; and that the atoms of the different
elements have different iveights.

Now if, when substances act upon one another/ the
action takes place between these atoms, and consists either
in a union or separation of the atoms, then it is easy to
understand why compounds are formed according to the law
of definite and multiple proportions. If two elements whose
atoms have weights which are to each other as 2 to 9
combine so that one atom of the one combines with one
atom of the other, then the compound which is formed
will contain the elements in the proportion of 2 parts by
weight of the one to 9 parts by weight of the other ele-
ment. If they combine so that one atom of the first
element combines with two atoms of the other, then the
resulting compound will contain the elements in the pro-
portion of 2 parts by weight of the one to 18 parts by
weight of the other element.

* Hypotheses and theories are of great value to science, if founded
upon a thorough knowledge of the facts to which they relate. They
become dangerous when used by those who are not familiar with the
facts. The student who has not received a thorough scientific train-
ing should remember that theories and hypotheses, to be of value,
must be suggested, not by a superficial but by a thorough knowledge
of the facts.

126 TEE ELEMENTS OF GEEMISTBT.

Atomic Weights. — The weights of the elements which
have thus far been referred to as combining weights are, in
accordance with the atomic theory, the relative weights of
the atoms, or the atomic weights. The symbols of the
elements represent atoms of the elements. Thus, H repre-
sents an atom of hydrogen, 0 an atom of oxygen, etc. As
hydrogen enters into combination in smaller proportion
than any other element, its combining weight or atomic
weight is taken as the unit. When we say that the atomic
weight of oxygen is 16, we mean simply that the atom of
oxygen is 16 times heavier than that of hydrogen.

Molecules. — As the symbols of the elements represent
atoms, so the symbols of compounds represent combina-
tions of atoms. The symbol of hydrochloric acid, HC1,
represents, according to the theory, the smallest particle
of this substance that can exist. It is made up of an atom
of hydrogen and an atom of chlorine, which are combined
chemically. The symbols HN03J, H20, NH3 are intended
to represent the smallest particles of the compounds that
can exist. The smallest particle of nitric acid consists of
1 atom of nitrogen, 1 atom of hydrogen, and 3 atoms of
oxygen. These smallest particles of compounds are called
molecule*. The molecules are made up of atoms. The
weight of a molecule is equal to the sum of the weights of
the atoms of which it is composed.

Avogadro's Law. — A careful study of the conduct of
gases has led to the conclusion that equal volumes of all
gases under the same conditions of temperature and pres-
sure contain the same number of molecules. This is known
as Avogadro's law.

The Relative Weights of Molecules Determined by
Weighing Gases. — If Avogadro's law is true, then by

ATOMIC THEORY— VALENCE. 127

weighing equal volumes of gaseous substances we can
learn the relative weights of the molecules of these sub-
stances.

Atomic Weights Learned from Molecular Weights. — If
we knew the molecular weight of all compounds we could
easily determine the atomic weights of the elements. It
would only be necessary to select the smallest quantity of
an element which occurs in any of its compounds. Thus,
for example, if we were to examine all known oxygen com-
pounds that can be studied in the form of gas or vapor,
we should find that the smallest quantity of oxygen found
in any molecule is represented by 16.

Valence. — The formulas of the compounds thus far con-
sidered have all been determined by exactly the same
methods. On comparing the formulas of the simplest
hydrogen compounds of chlorine, oxygen, nitrogen, and
carbon a curious difference is observed. The formulas are

C1H, OH„ NH3, CH4.

According to the atomic theory these expressions mean
that the molecule of hydrochloric acid consists of 1 atom
of chlorine combined with 1 atom of hydrogen; the mole-
cule of water consists of 1 atom of oxygen combined with
2 atoms of hydrogen; the molecule of ammonia of 1 atom
of nitrogen and 3 atoms of hydrogen; and the molecule of
marsh-gas of 1 atom of carbon and 4 atoms of hydrogen.
It appears, therefore, that the atom of oxygen can hold in
combination twice as many hydrogen atoms as the atom of
chlorine can; that the atom of nitrogen can hold three
times as many; and the atom of carbon four times as
many. Other atoms differ from one another in the same
way.

128 THE ELEMENTS OF CHEMISTRY,

That property of an element by virtue of which its atom
can hold in combination a definite number of other atoms
is called valence.

Kinds of Elements. — The smallest power, as far as the
number of other atoms which it can hold in combination is
concerned, is that of the chlorine atom. As one chlorine
atom can hold but one hydrogen atom in combination, so
one hydrogen atom can hold but one chlorine atom.
Either the hydrogen atom or the chlorine atom may be
taken as an example of the simplest kind of atom. An
element like hydrogen or chlorine is called a univalent
element; an element like oxygen whose atom can hold two
unit atoms in combination is called a Mvalent element; an
element like nitrogen whose atom can hold three unit
atoms in combination is called a trivalent element; and an
element like carbon whose atom can hold four unit atoms
in combination is called a quadrivalent element. Most
elements belong to one or the other of these four classes.

[Calcium forms with chlorine the compound CaCl2.
What is the valence of calcium ? Potassium and sodium
form chlorides of the formulas KC1 and NaCl respectively.
What is the valence of these elements ? Sulphur forms
with hydrogen a compound of the formula SH2. What is
the valence of sulphur ?]

Displacing Power of the Elements. — In the formation of
salts you have seen that the hydrogen of acids is displaced
by metals. In such cases one atom of a univalent metal
takes the place of one atom of hydrogen, one atom of
a bivalent metal takes the place of two atoms of hydrogen,
etc. Thus potassium and sodium are univalent. In the
formation of potassium nitrate from nitric acid, HNO„
one atom of potassium displaces one atom of hydrogen in

CLASSIFICATION OF TEE ELEMENTS. 129

the molecule of nitric acid, forming the salt KN03. So
also sodium nitrate is N~aN03. In the molecule of sul-
phuric acid, H2S04, there are two atoms of hydrogen. To
displace these, two atoms of a univalent element are re-
quired. Thus, potassium sulphate is K2S04, and sodium
sulphate is Na2S04. Examples of salts containing bivalent
metals are the following: zinc sulphate, ZnS04, in which
one atom of bivalent zinc has displaced the two atoms of
hydrogen of the sulphuric acid ; barium sulphate, BaS04,
in which one atom of bivalent barium has displaced the two
atoms of hydrogen of sulphuric acid. When a bivalent
metal forms a salt with an acid like nitric acid, which con-
tains but one atom of hydrogen in the molecule, it is be-
lieved that one atom of the metal acts upon two molecules
of the acid, thus :

Pii , HN03 _ Pii j NO, , H

or

Cu + 2H¥03 = Cu(NO,)9 + H2.

The formula of zinc nitrate is similar, viz., Zn(N03)2.
In the case of trivalent elements the matter is a little more
complicated, but still simple enough if it be borne in mind
that a univalent atom displaces one atom of hydrogen ; a
bivalent atom displaces two atoms of hydrogen ; a trivalent
atom displaces three atoms of hydrogen, etc.

Classification or the Elements.

Acid Properties and Basic Properties. — The chemical

properties which force themselves upon our attention most

prominently in whatever field of chemistry we may be

working are those which are known as acid properties and

9

130 THE ELEMENTS OF CHEMISTRY.

basic properties. As has already been pointed out, these
two kinds of properties are the opposite of each other. No
matter how much chemistry may grow, it is certain that
the distinction between these two kinds of properties will
always be recognized as important.

Acid-forming Elements and Base-forming Elements. — In
general, both acids and bases contain hydrogen and oxygen,
There are some elements ivhose compounds ivith hydrogen
and oxygen have basic properties, and others whose com-
pounds with hydrogen and oxygen have acid properties
This important fact may be used as the basis of a partial
classification of the elements. According to this, we have
(1) acid-forming elements and (2) base-forming elements.
Examples of the first class are chlorine, nitrogen, and sul-
phur. Examples of the second class are sodium, calcium,
magnesium, etc. The last mentioned are generally called
metals, and the acid-forming elements are generally called
non-metals.

Families of Elements. — Another important fact which is
soon recognized in studying the elements is that they fall
into families according to their chemical properties, the
members of the same family showing striking resemblances
among one another. Thus, there is the chlorine family,
which includes, besides chlorine itself, bromine, iodine,
and fluorine. Further, there is the sulphur family, con-
sisting of the closely related elements sulphur, selenium,
and tellurium ; besides other families. In all these cases
the resemblance between members of the same family is
striking.

Families of the Acid- forming Elements. — First, we shall
have the following families to deal with :

CLASSIFICATION OF THE ELEMENTS. 131

Chlorine Family.

Sulphur Family.

Nitrogen Family.

Carbon Family.

Chlorine,

Sulphur,

Nitrogen,

Carbon,

Bromine,

Selenium,

Phosphorus,

Silicon.

Iodine,

Tellurium.

Arsenic,

Fluorine.

Antimony.

As the object of your present study is to get a general idea
of the principles of chemistry, it will not be necessary to
go into details in dealing with these families. One member
of each family, except the sulphur family, having been
treated comparatively fully, the other members may be
treated briefly. The members of the sulphur family re-
semble oxygen somewhat, but also differ from it in many
respects. It will thus be possible to get a clearer idea of
the principles of chemistry than by attempting to study a
laro;e number of facts.

132 THE ELEMENTS OF CHEMISTRY.

OHAPTEK XV.40KZL

THE CHLORINE FAMILY: CHLORINE, BROMINE,
IODINE, FLUORINE.

Introduction. — The three members of this family which
show the most marked resemblance are chlorine, bro-
mine, and iodine. Fluorine is not known in the uncom-
bined state. Its compounds, however, resemble the com-
pounds of chlorine, and henco the element is generally
included in this family.

Bromine {At. Wt. 80). — This element occurs in nature
in company with chlorine. Chlorine, as has been stated,
occurs mostly in combination with sodium, as sodium
chloride, or common salt. In several of the great salt-
beds there is some bromine in the form of sodium bromide,
NaBr, and in some places it occurs as potassium bromide,
KBr.

Preparation of Bromine. — The method is the same as
that made use of for extracting chlorine. In order to get
chlorine out of common salt, the salt is first converted into
hydrochloric acid, and this is then oxidized. So, too, in
order to get bromine out of sodium bromide, the bromide
must first be converted into hydrobromic acid, and this
then oxidized. The reactions are

2NaBr + H2S04 = Na2S04 + 2HBr ;
2HBr + 0 = H20 + 2Br.

THE CHLOBINE FAMILY. 133

Properties of Bromine. — Bromine is a heavy dark-red
liquid at ordinary temperatures which is easily converted
into a brownish red vapor. It has an extremely dis-
agreeable odor. Hence its name from a Greek word mean-
ing a stench. Its properties are, in general, like those of
chlorine. It acts violently upon organic substances. It
attacks the skin and the membranes lining the passages of
the throat and lungs. Wounds caused by the liquid com-
ing in contact with the skin are painful and heal with dif-
ficulty. It must, therefore, be handled with great care. It
combines with many elements directly and with great
energy, its compounds with other elements being called
bromides. While acting in general in the same way as
chlorine, it is a somewhat weaker element, so that chlorine
drives it out of its compounds and sets it free.

Experiment 82. — Mix together about a gram of potassium
bromide and two grams of manganese dioxide. Pour upon the
mixture in a good-sized test-tube sufficient dilute sulphuric acid
to cover it. Heat gently. What do you observe ? Perform this
experiment where there is a good draught.

Hydrobromic Acid, HBr. — The only compound which

bromine forms with hydrogen alone is hydrobromic acid.

This is in all respects very much like hydrochloric acid.

Experiment 83. — In a test-tube put a few crystals of potassium
bromide. Pour on them a few drops of concentrated sulphuric
acid. The white fumes of hydrobromic acid and the reddish-
brown vapor of bromine are noticed. Treat a few crystals of
potassium or sodium chloride in the same way. What difference
is there between the two cases ? The explanation of the difference
observed is that sulphuric acid decomposes hydrobromic acid, set-
ting bromine free, while it does not decompose hydrochloric acid.

Compounds with Hydrogen and Oxygen. — With hydrogen

and oxygen bromine forms compounds which resemble very

closely those which chlorine forms with the same elements.

134 THE ELEMENTS OF CHEMISTBY.

The principal ones are bromic, HBr03, and hypolromous
acids, HBrO, which are like chloric and hypochlorous acids.

Iodine, I (At. Wt. 127). — This element occurs in nature
in combination with sodium, in company with chlorine and
bromine, but in smaller quantity than either. It is also
found in larger quantity in sea-plants. It is obtained
largely from the latter source. On the coasts of Scotland
and France the sea-weed which is thrown up by storms is
gathered, dried, and burned. The organic portions are thus
destroyed [what is the meaning of the word destroyed used
in this sense?], and the mineral or earthy portions are left
behind as ashes. The incombustible residue is called kelp.
It contains sodium iodide. At present, in some parts of the
ocean, sea- weed is cultivated for the sake of the iodine
which it yields. Chili saltpetre, or the natural sodium
nitrate found in Chili, contains some sodium iodide, and
of late this has furnished a considerable quantity of the
iodine of commerce.

Preparation of Iodine. — Iodine is prepared from sodium
iodide, just as chlorine and bromine are prepared from their
compounds with sodium and potassium.

Properties of Iodine. — At ordinary temperatures iodine is
a grayish- black, crystallized solid. It melts easily and boils,
forming a yiolet-colored vapor.

Experiment 84. — Mix about 1 gram potassium iodide with
about twice its weight of manganese dioxide. Treat with a little
sulphuric acid in a test-tube. Heat gently. Gradually the tube
will be filled with the beautiful colored vapor of iodine. In the
upper part of the tube some of the iodine will be deposited in the
form of crystals of a grayish-black color.

Iodine dissolves slightly in water, easily in alcohol, and
easily in a water solution of potassium iodide.

E

THE CHLOBmE FAMILY, 135

Ixperiment 85. — Make solutions of iodine in water, in alcohol,
and in a water solution of potassium iodide. Use small quantities
in test-tubes.

When a solution containing free iodine is treated with a
little starch-paste the solution turns blue,, in consequence
of the formation of a complicated compound of starch and
iodine. Bromine and chlorine do not form blue compounds.
Advantage is taken of this fact to distinguish between
iodine and other members of the family.

Experiment 86. — Make some starch-paste by covering a few
grains of starch in a porcelain evapo rating-dish with cold water,
grinding this to a paste, and pouring 200-300 cc. boiling hot
water on it. After cooling add a little of this paste to a dilute
water solution of iodine. What change takes place ? Now add
a little of the paste to a diluted water solution of potassium iodide.
Is there any change of color ? Acid a drop or two of a solution
of chlorine in water. What takes place ? Explain what you have
seen. Does chlorine alone form a blue compound with starch ?

Hydriodic Acid, HI,, is analogous to hydrochloric and
hydrobromic acids. It is set free from the iodides by treat-
ing them with sulphuric acid; but it is even more unstable
than hydrobromic acid, and hence breaks up into hydrogen
and iodine. The iodine is set free, while the hydrogen
acts on the sulphuric acid, as it does in the case of hydro-
bromic acid.

Experiment 87 . — Treat a few small crystals of potassium iodide
with sulphuric acid. [What do you notice ?] Compare with the
results obtained when potassium bromide and sodium chloride are
used.

Fluorine occurs in nature in large quantity, and widely
distributed, but always in combination with other elements.
It is found chiefly in combination with calcium, as fluor-
spar, or calcium fluoride, CaF2, and in combination with
sodium and aluminium, as cryolite, a mineral which oc-

136 THE ELEMENTS OF CHEMISTRY.

curs abundantly in Greenland, and has the composition
3NaF . A1F3, being a complex compound of sodium fluoride
and aluminium fluoride. The element fluorine has not
been obtained in the free state.

Hydrofluoric Acid, HP, is made from fluor-spar by treat-
ing it with sulphuric acid. The action is of the same char-
acter as that which takes place when hydrochloric acid is
liberated from sodium chloride:

CaF2 + H2S04 = OaS04 + 2HF.

It is a colorless gas, with strong acid properties. 11
greatly irritates the membranes lining the throat and lungs
and hence care should be taken not to inhale it. It acts
upon glass, dissolving it, and must therefore be kept in
vessels of rubber, lead, or platinum, upon which it does no
act.

Etching on Glass. — The acid is used for etching on glass,
particularly for marking scales on thermometers, barome-
ters, and other graduated glass instruments. A solution of
the gas in water is manufactured for this purpose and kept
in rubber bottles.

Experiment 88. — In a lead or platinum vessel put a few grams
(5-6) of powdered fluor-spar, and pour on it enough concentrated
sulphuric acid to make a thick paste. Cover the surface of a
piece of glass with a thin layer of wax or paraffin, and through
this scratch some letters or figures, so as to leave the glass ex-
posed where the scratches are made. Put the glass with the
waxed side downward over the vessel containing the fluor-spar,
and let it stand for some hours. Then take off the glass, scrape
off the coating, and the figures which were marked through the
wax or paraffin will be found etched on the glass.

Comparison of the Members of the Chlorine Family. — In
considering, first, the physical properties of these elements,
you notice that all, with the exception of fluorine, form

THE CHLORINE FAMILY. 137

colored gases or vapors. At ordinary temperatures chlorine
is a gas, bromine a liquid, and iodine a solid. In regard to
their chemical conduct, it may be said that, in general,
fluorine is the most active; chlorine comes next in order,
then bromine, and lastly iodine.

Their Compounds. — The compounds formed by the three
elements chlorine, bromine, and iodine with hydrogen and
oxygen have analogous compositions, and are formed by
analogous reactions. Thus, there are the hydrogen com-
pounds:

HC1, HBr, and HI;

and the compounds with hydrogen and oxygen:

HCIO, HBrO. —
HC102. — —

HC103, HBr03, HI03.
HC104, HBr04, HI04.

Relations between the Atomic Weights. — On comparing
the atomic weights of chlorine, bromine, and iodine, it
will be seen that the atomic weight of bromine, which is
80, is nearly the mean of the atomic weights of chlorine
and iodine.

35.5 + 127 = 162.5;

At. Wt. of At. Wt. of

chlorine. iodine.

and — ^— = 81.25, which is nearly the atomic weight of

bromine.

Relation between the Properties of the Elements and
their Atomic Weights. — The properties of the three ele-
ments chlorine, bromine, and iodine vary with the varia-

138 THE ELEMENTS OF CHEMISTRY.

tions in their atomic weights, or with the weights of their
atoms. The gradation in properties takes place in the
order chlorine, bromine, iodine, and this is also the order
in which the atomic weights increase. This may be a
mere coincidence, but we shall find that in the other fami-
lies there are similar indications of a close connection be-
tween the weights of the atoms of the elements and their
physical and chemical properties.

THE SULPHUR FAMILY. 133

CHAPTER XVI.

THE SULPHUR FAMILY: SULPHUR, SELEKEUM,
TELLURIUM.

Sulphur, S {At. Wt. 32). — The principal member of the
family is sulphur. In nature it is frequently found ac-
companied by small quantities of selenium, and sometimes
by tellurium. It has been known in the elementary form
from the earliest times, for the reason that it occurs abun-
dantly in this form in nature. It is found particularly in
the neighborhood of volcanoes, as in Sicily, which is the
chief source of the sulphur of commerce. It occurs, fur-
ther, in combination with many metals as sulphides, — as
in iron pyrites, FeS2; copper pyrites, FeCuS2; galenite,
PbS, etc. ; in combination with metals and oxygen as sul-
phates, — for example, as calcmm sulphate, or gypsum,
CaS04 + 2H20; barium sulphate, or heavy spar, BaS04;
lead sulphate, PbS04; and in a few vegetable and animal
products in combination with carbon, hydrogen, and, gene-
rally, with nitrogen.

Extraction of Sulphur from its Ores. — When taken from
the mines, sulphur is mixed with many earthy substances
from which it must be separated. This separation is ac-
complished by piling the ore in such a way as to leave
passages for air. The piles are covered with some material
to prevent free access of air, and the mass is then lighted
below. A part of the sulphur burns, and the heat thus
furnished melts the rest of the sulphur. The molten sul-

140 THE ELEMENTS OF CHEMISTRY.

phur runs doAfn to the bottom of the pile, and is drawn off
from time to time.

[If the pile were not protected from free access of air
what would become of the sulphur? What analogy is
there between this process and that made use of in making
charcoal? What are the essential differences between the
two processes?]

How Sulphur is Refined. — The crude brimstone first ob-
tained is afterwards refined by distillation, and it is this
distilled sulphur which is met with in commerce under the
names "roll brimstone/' "stick sulphur/' and "flowers of
sulphur/' The distillation is carried on in earthenware
retorts connected with large chambers of brick-work.
When the vapor of sulphur first comes oyer into the con-
densing chamber it is suddenly cooled, and hence deposited
in the form of fine powder. This is what is called " flowers
of sulphur." After the distillation has continued for some
time the vapor condenses in the form of a liquid, which
collects at the bottom of the chamber. This is drawn off
into wooden moulds and takes the form of "roll brim-
stone" or "stick sulphur."

Properties of Sulphur. — Sulphur is a yellow, brittle sub-
stance which at — 50° is almost colorless. It melts at
111°, forming a thin, straw-colored liquid. When heated
to a higher temperature it becomes darker and darker in
color, and at 200° to 250° it is so thick that the vessel con-
taining it may be turned upside down without danger of
running out. Finally, at 440° it boils and is then con-
verted into brownish-yellow vapor.

Experiment 89. — Distil about 10 grams of roll sulphur from
an ordinary glass retort. The retort need not be connected with
a condenser. Notice the changes above described. Collect the

THE STTLPHTTB FAMILY. 141

liquid sulphur which passes over in a beaker-glass containing
cold water.

Crystals of Sulphur. — When molten sulphur solidifies, or
when it is deposited from a solution, its particles arrange
themselves in regular forms called crystals. But, strange
to say, the crystals formed from molten sulphur are en-
tirely different from those deposited from solut: .ns of sul-
phur. Substances which crystallize in two distinct forms
are called dimorphous. Carbon, like sulphur, crystallizes
in two different forms [what are they?], and is hence di-
morphous.

Experiment 90. — In a covered sand or Hessian crucible melt
about 20 grams of roll sulphur. Let it cool slowly, and when a
thin crust has formed on the surface make a hole through this
and pour out the liquid part of the sulphur. The inside of the
crucible will be found lined with honey-yellow needles. Take
out a few crystals and examine them. — Are they brittle or elas-
tic? What is their color? Are they opaque, transparent, or
translucent ? — Lay the crucible aside, and in the course of a few
days again examine the crystals. — What changes, if any, have
taken place ?

Solution of Sulphur. — Sulphur is insoluble in water,
slightly soluble in alcohol and ether. It dissolves in the
liquid compound of carbon and sulphur known as carbon
disulphide, CS2, and from this solution it is deposited in
crystals quite different from those obtained in Experiment
90.

Experiment 91. — Dissolve 2 to 3 grams roll sulphur in 5 to 10
cc. carbon disulphide. Put the solution in a shallow vessel, and
allow the carbon disulphide to evaporate by standing in the
air. What is the appearance of the crystals? Are they dark
yellow or bright yellow ? Are they brittle or elastic ? [State in
tabular form the properties of the two allot ropic forms of sul-
phur.]

142 T3E ELBMENTB OF CBEMISTBT.

Chemical Conduct of Sulphur. — Sulphur combines with
oxygen when heated to a sufficiently high temperature.
The product is sulphur dioxide, S02. [Is there any anal-
ogy between carbon and sulphur in this respect ?] It com-
bines readily with most metals, forming sulphides. Its
combination with iron has already been shown in Experi-
ment 12. It also combines with copper, the act being
accompanied by light and heat.

Experiment 92. — In a wide test-tube heat some sulphur to
boiling. Introduce into it small pieces of copper-foil or sheet-
copper. Or hold a narrow piece of sheet- copper so that the end
just dips into the boiling sulphur. What evidence have you that
action takes place ?

Hydrogen Sulphide, Sulphuretted Hydrogen, H2S. — When
hydrogen is passed over highly heated sulphur the two ele-
ments combine to form hydrogen sulphide. [Is there any
analogy between this process and the formation of water by
the burning of hydrogen ?] This compound of sulphur
and hydrogen occurs in nature in solution in the so-called
"sulphur waters," which are met with in many parts of
this country as well as in other countries. It also issues
from the earth in some places. It is formed by heating or-
ganic substances which contain sulphur, just as water is
formed by heating organic substances which contain oxy-
gen, and ammonia by heating such as contain nitrogen. It
is formed, further, by decomposition of organic substances
which contain sulphur, as, for example, the albumen of
eggs. The odor of rotten eggs is partly due to the forma-
tion of hydrogen sulphide. [How is it that paraffin, p. 107,
heated with sulphur gives off hydrogen sulphide ?]

Preparation of Hydrogen Sulphide. — It is made in the
laboratory by heating a sulphide with an acid. When sul-

THE SULPHUR FAMILY.

143

phuric acid acts upon iron sulphide, hydrogen sulphide is
given off thus:

FeS + H2S04 = FeS04 + H2S.

Hydrochloric acid acts in a similar way:

FeS + 2HC1 = FeCl2 + H2S.

Experiment 93. — Arrange an apparatus as shown in Fig. 36.
Put a small handful of sulphide of iron, FeS, in the flask, and
pour dilute sulphuric acid upon it. Pass the gas through a little
water contained in the wash-cylinder A. Pass some of the gas
into water. What evidence have you that it dissolves ? — Collect
some by displacement of air. It is heavier than air (specific grav-
ity 1.178). Should the vessel be placed with the mouth down or
up ? Set fire to some of the gas contained in a cylinder. If there
is free access of air the sulphur burns to sulphur dioxide, and the
hydrogen to water.

Fig. 36.

Properties of Hydrogen Sulphide. — Hydrogen sulphide,
or, as it is commonly called, sulphuretted hydrogen, is a
colorless, transparent gas. It has a disagreeable odor,
somewhat resembling that of rotten eggs. It is poisonous

144 THE ELEMENTS OF CHEMISTRY.

when inhaled in any quantity. It dissolves in water, form-
ing a solution which has the odor of the gas. Most metals
when heated in the gas are converted into sulphides.
Thus, when it is passed over heated iron this reaction takes
place:

Fe + H2S = FeS + H2.

[What takes place when water vapor is passed over
heated iron ?]

Precipitation of Sulphides. — Many of the sulphides are

insoluble in water. Hence, when hydrogen sulphide is

passed through solutions containing metals in the form of

soluble salts, the insoluble sulphides are thrown down, or

precipitated.

Experiment 94. — Pass hydrogen sulphide successively through
solutions containing a little lead nitrate, zinc sulphate, and
arsenic prepared by dissolving a little white arsenic, or arsenic
trioxide, As203, in dilute hydrochloric acid. What do you
observe in each case? — The substances formed are respectively
the sulphides of lead, zinc, and arsenic. The reaction in the case
of zinc sulphate is represented thus:

ZnS04 + H2S = ZnS + H2S04.

Chemical Analysis. — In dealing with chemical substances
the first thing we have to determine is their composition,
or, in other words, we have to analyze them. For this
purpose we must first know the properties of the elements
and their conduct towards chemical substances. To facili-
tate the process of analysis the mixture to be examined *s
usually brought into solution and then treated successively
with certain substances, the effect being observed in each
case. Suppose we had a solution containing most of the
metallic elements in the form of salts. If we were to pass
hydrogen sulphide through this solution, some of the met-

TEE SULPHUR FAMILY. 145

als would be precipitated as sulphides, while others would
remain in solution, as their sulphides are soluble. The
precipitated sulphides could then be filtered off and exam-
ined, and the filtered solution also could be further exam-
ined. Hydrogen sulphide is constantly made use of in the
laboratory for the purposes of analysis,

Compounds of Sulphue with Oxygen, and with
Hydrogen and Oxygen.

Formation of the Compounds of Sulphur. — When sulphur
burns in the air, the dioxide, S02, is formed. Under cer-
tain conditions the dioxide combines with more oxygen,
forming the trioxide, S03. When sulphur dioxide acts
upon water, sulphurous acid is formed:

SO, + H20 = H2S03.

[Yfhat analogy is there between the acid thus formed
and carbonic acid?]

When the trioxide combines with water, sulphuric acid
is formed:

S08 + H20 = H2S04.

Sulphur Dioxide, S02. — This compound is formed by
burning sulphur in the air or in oxygen. It issues from
volcanoes in large quantities. It is best prepared by heat-
ing copper with sulphuric acid. We should naturally
expect the copper simply to take the place of the hydrogen
of the acid, thus:

Cu + H2S04 = CuS04 + 2H.

Probably this action takes place first. But the hydrogen
10

146 THE ELEMENTS OF CHEMISTRY.

acts upon the sulphuric acid, reducing it and forming sul-
phur dioxide:

H2S04 + 2H = 2H,0 + S02.

[Compare the action of copper on sulphuric acid with
that of copper on nitric acid. What analogy is there be-
tween the two cases?]

Experiment 95. — Put eight or ten pieces of sheet-copper, one
to two inches long and about half an inch wide, into a 500-cc.
flask; pour 15 to 20 cc. concentrated sulphuric acid upon it. On
heating, sulphur dioxide will be evolved. The moment the gas
begins to come off, lower the flame, and keep it at such a height
that the evolution is regular and not too active. Pass some of
the gas into a bottle containing water. Collect a vessel full by
displacement of air. It is more than twice as heavy as air. See
whether the gas will burn or support combustion.

Properties of Sulphur Dioxide. — Sulphur dioxide is a
colorless gas of an unpleasant, suffocating odor, familiar
to every one as that of burning sulphur-matches. Water
dissolves it readily. It bleaches readily, and stops fermen-
tation.

Experiment 96. — Burn a little sulphur in a porcelain crucible
under a bell- jar. Place over the crucible on a tripod some
flowers. In the atmosphere of sulphur dioxide the flowers will
be bleached.

Uses of Sulphur Dioxide. — It is used extensively for the
purpose of bleaching wool, silk, straw, paper, etc.; and,
further, to preserve liquids which have a tendency to under-
go fermentation. If left in the air, fruit-juices become
sour in consequence of fermentation. As sulphur dioxide
prevents fermentation, the juices are kept sweet if treated
with something which gives off the gas, as, for example, a
sulphite. The principal use of sulphur dioxide is in the

THE SULPHUR FAMILY. 147

manufacture of sulphuric acid. For this purpose it is
made in enormous quantities.

Sulphurous Acid and Sulphites. — The solution of sulphur
dioxide in water has acid properties, and contains the acid
H2S03. By neutralizing the solution with bases, the
sulphites, or salts of sulphurous acid, are obtained. The
sulphites are analogous to the carbonates in composition,
and suffer the same decomposition when treated with acids.
When a carbonate is treated with an acid, carbon dioxide
is given off. So, also, when a sulphite is treated with an
acid, sulphur dioxide is given off:

Na2S03 + H2S04 = Na2S04 + H20 + SO,;
NaaSO, + 2H01 = 2NaCl + H20 + S02.

Sulphuric Acid, H2S04. — Salts of sulphuric acid are found
in nature, as gypsum, heavy spar, etc. It cannot easily be
prepared from its salts, as hydrochloric and nitric acids
are prepared, and is made exclusively by oxidizing sulphur
dioxide in the presence of water, or, in other words, by
oxidizing sulphurous acid. The reactions involved in the
manufacture of sulphuric acid are:

S + 02 = S02;

S02 + H20 = H2S03;
H2S03 + 0 = H2S04.

The last reaction cannot readily be effected directly by the
action of the oxygen of the air, but an extremely interest-
ing method has been devised by which the oxygen of the
air is constantly transferred to the sulphurous apd.

How Nitric Oxide Acts in Oxidizing Sulphurous Acid. —
The method depends partly upon the power of nitric oxide,

•1

148 THE ELEMENTS OF CHEMISTRY.

NO, to combine directly with the oxygen of the air to
form nitrogen peroxide, N02. Nitrogen peroxide gives up
half its oxygen to sulphurous acid, and is itself thus
reduced to nitric oxide. If, therefore, sulphur dioxide,
water, and nitrogen peroxide be brought together, the first
action is represented thus:

SO, + H20 + N02 = H2S04 + NO.

Now, if air be supplied, the nitric oxide will be converted
into the peroxide:

NO + 0 = N02.

The peroxide acting upon a further quantity of sulphur
dioxide and water is again reduced, and so on indefinitely.
It will thus be seen that, starting with a small' quantity of
nitric oxide, it should be possible to convert a large quantity
of sulphur dioxide into sulphuric acid.

Manufacture of Sulphuric Acid. — In the manufacture of
sulphuric acid sulphur or iron pyrites, FeS2, is burned.
In the former case, the only product of the combustion is
sulphur dioxide; in the latter case, the sulphur forms sul-
phur dioxide, and the iron is converted into an oxide,
Fe208. The sulphur dioxide thus formed is conducted
into large chambers lined with lead, for the reason that
sulphuric acid does not act upon lead, while it does act
upon most other common metals. Instead of starting with
nitric oxide, nitric acid is passed into the chambers, and
water in the form of steam. The first action between the
nitric acid, steam, and sulphur dioxide is this:

2HN03 + 3SO, + 2H30 = 3H2S04 + 2N0.

THE SULPHUR FAMILY.

149

From this point sulphur dioxide, water, and nitric oxide
are brought into action, and the chief reactions are those
described above.

A Leaden Chamber. — The arrangement of a leaden
chamber is shown in Fig. 37. The furnace in which the
sulphur or iron ppites is burned is represented by /.
Steam from the boiler b is forced into the chamber through

Fig. 37.

jets. The nitric acid is formed from Chili saltpetre and
sulphuric acid in the furnace n. A good draught is kept
up by means of a high chimney.

Ordinary Sulphuric Acid: Oil of Vitriol. — The acid ob-
tained from the chambers is evaporated in lead pans, and
afterwards in platinum or glass. The strong acid thus
obtained is the concentrated sulphuric acid of commerce,
which is commonly called oil of vitriol. It is an oily liquid,
usually somewhat colored by impurities.

The pxire acid is a colorless liquid at ordinary temper-
atures. When cooled down it forms crystals. It decom-
poses the salts of most other acids, setting the acids free
and forming sulphates. You have already had illustrations
of this power in the liberation of nitric and hydrochloric
acids from their salts by treatment with sulphuric acid.

[Give the equations representing the action which takes

150 THE ELEMENTS OF CHEMISTRY.

place when common salt and potassium nitrate are treated
with sulphuric acid.]

Sulphuric Acid Combines with Water. — Sulphuric acid
has a very strong tendency to absorb water and form com-
pounds with it. A great deal of heat is formed in this
action. This fact has been repeatedly illustrated in ex-
periments already performed; and attention has been
called to the necessity for caution in mixing the liquids.
The acid acts upon organic substances containing hydrogen
and oxygen, and extracts them in the proportions to form
water. A piece of wood is charred, if put in the acid, in
consequence of the abstraction of hydrogen and oxygen.
[How is wood charred in the preparation of charcoal? Is
there any analogy between the preparation of charcoal in
the ordinary way and by the action of sulphuric acid?]

Wounds caused by sulphuric acid are painful and heal
with difficulty.

Importance of Sulphuric Acid. — Sulphuric acid is the
most important manufactured chemical substance. Most
chemical industries depend upon it. Among the many
uses to which it is put are the making of "soda" or
sodium carbonate, which is necessary for the manufacture
of soap and glass; the making of phosphorus; of artificial
fertilizers; the refining of petroleum, etc., etc. In 1883
there were manufactured 300,000 tons of sulphuric acid in
the United States, and over 900,000 tons in Great Britain.

Monobasic and Dibasic Acids. — Sulphuric acid differs
markedly from nitric and hydrochloric acids in one respect.
It has the power to form two different salts with the same
metal, in one of which there is relatively twice as much of
the metallic element as in the other. If to a given quan-
tity of sulphuric acid there be added only half the quantity

THE SULPHUR FAMILY. 151

of caustic potash required to neutralize it, a salt is formed
which crystallizes. It has the composition represented by
the formula KHS04. If nitric acid be treated in the same'
way, only half the acid is acted on, and this forms ordi-
nary potassium nitrate, KN03, the rest of the acid being
left unacted upon. In the case of sulphuric acid two
reactions are possible, viz. :

H2S04 + KOH = KHS04 + H20;

H2S04 + 2KOH ±= K2S04 + 2H20.

In the case of nitric acid only one reaction seems to be
possible :

HN03 + KOH = KN03 + H03.

Acids which, like sulphuric acid, have the power to form
two salts with the same metal are called dibasic acids.
Acids which, like nitric acid, have the power to form only
one salt with the same metal are called monobasic acids.
This power is connected with the number of replaceable
hydrogen atoms contained in the molecule of the acid.
An acid containing two replaceable hydrogen atoms in its
molecule is dibasic ; one containing only one replaceable
hydrogen atom in its molecule is monobasic.

Acid, Neutral, and Normal Salts. — A dibasic acid yields
two classes of salts : (1) those in which all the hydrogen is
replaced, and (2) those in which half the hydrogen is re-
placed by metal. The former are called normal salts, the
latter acid salts. Normal salts are generally neutral, and
are sometimes called neutral salts.

Carbon Bisulphide, CS2. — Sulphur forms with carbon a
compound called carbon disulphide, which has the compo-

152 THE ELEMENTS OF CHEMISTRY.

tion 0S2. It is made by bringing carbon and sulphur to-
gether at high temperatures. It is a liquid which boils at
47°. That it dissolves sulphur has been shown in Experi-
ments 11 and 91. It also dissolves many other substances.

Selenium, Tellurium, and their Compounds. — These elej
ments are rarely met with. In general their properties are
very similar to those of sulphur, and they form compounds
analogous to the principal compounds of sulphur.

Relations between the Atomic Weights of Sulphur, Sele-
nium, and Tellurium. — The relation between the atomic
weights of the members of the sulphur family is like that
already noticed between the atomic weights of the members
of the chlorine family. It is shown thus :

32 + 125.2 =157;

At. Wt. of At. Wt. of

sulphur. tellurium.

157 2
and — ^— = 78.6, which is nearly 79, the atomic weight of

selenium.

THE NITROGEN FAMILY. 153

CHAPTER XVII.

THE NITROGEN FAMILY: NITROGEN, PHOSPHORUS,
ARSENIC, AND ANTIMONY.

Boikxn" and Silicon.

Phosphorus, P (At. Wt. 31). — Phosphorus occurs in the
form of phosphates, or salts of phosphoric acid. The chief
of these is calcium phosphate, which is the principal con-
stituent of the minerals phosphorite and apatite, and of the
ashes of bones.

Phosphorus Made from Bones. — It is made from bone-ash,
which contains a large proportion of calcium phosphate.
The ash is first mixed with sulphuric acid. Then the
compound thus obtained is mixed with charcoal and
heated, when phosphorus distils over. It is cast into
sticks under water, and kept under water.

Properties. — It is colorless or slightly yellow and trans-
lucent. At ordinary temperatures it can be cut like wax,
but it becomes hard and brittle at lower temperatures. It
melts at 44°, and boils at 290°. Unless carefully protected
from the light its appearance changes. It becomes opaque
and dark in color, and finally dark red. This change can
be hastened by heating the phosphorus in a sealed tube to
250°. Ordinary phosphorus is insoluble in water, but solu-
ble in carbon disulphide. In contact with the air it gives
off fumes which emit a pale light visible in a dark room.
It takes fire when rubbed or cut, and must hence b§

154 THE ELEMENTS OF CHEMISTRY.

handled with great care. It should always be cut under
water, and never held in the hand. It not only combines
with oxygen easily, but with other elements, such as chlo-
rine, bromine, and iodine.

Experiment 97. — Bring together in a porcelain crucible or
evaporating-dish a little phosphorus and iodine. It will be seen
that simple contact is sufficient to cause the two substances to
act upon each other. Direct combination takes place, and the
action is accompanied by light and heat.

Phosphorus is very poisonous. Its vapor produces a
disease of the bones.

Red Phosphorus. — The red substance formed when ordi-
nary phosphorus is left in the light, or heated without ac-
cess of air, is a second variety of phosphorus, known as red
phosphorus. This differs from ordinary phosphorus as
much as graphite differs from the diamond. Ordinary
phosphorus is very active, combining readily with oxygen;
it is soluble in carbon disulphide; and is poisonous. Eed
phosphorus, on the other hand, is inactive. It does not
change in the air, and requires to be heated to a compara-
tively high temperature before it will combine with oxygen;
it is insoluble in carbon disulphide, and is not poisonous.
It is converted into the ordinary variety when heated to
about 300°. [Make out a tabular comparison of the pro-
perties of the two allotropic forms of phosphorus.]

Uses of Phosphorus. — The principal use of phosphorus is
in the manufacture of matches. Ordinary friction-matches
are tipped with a mixture of phosphorus, glue, and potas-
sium chlorate. " Safety-matches" are usually tipped with
potassium chlorate and antimony sulphide. The surface
upon which they are rubbed is made of red phosphorus,
black oxide of manganese, and glue. Mixed with flour,
phosphorus is frequently used as a rat-poison?

TEE NITBOGEN FAMILY. 155

Compounds of Phosphorus with Oxygen and with Hydro-
gen and Oxygen. — When phosphorus is burned in the air
or in oxygen it is converted into the oxide, P205. This
combines with water in different proportions, forming two
distinct acids, known as metaphosphoric and orthophospho-
ric acids :

P.O.+ H20= 2HPO,;

Metaphosphoric acid.

P,06 + 3HsO=2HaP04.

Orthophosphoric acid.

Orthophosphoric or Ordinary Phosphoric Acid, H3P04, is

the principal compound of phosphorus. It is the final
product of the action of air and moisture on phosphorus.
As has been stated, it occurs in nature as the calcium salt
in phosphorite and apatite. This salt is also the chief
constituent of bone-ash. It is a solid crystallized sub-
stance, and is made by treating bone-ash with sulphuric
acid, or by oxidizing phosphorus. It has the power of
forming three distinct salts with the same metal, and is
hence called tribasic. With sodium, for example, it forms
the three salts Na3P04, NaaHP04, and NaH2P04. Its
normal calcium salt — that is to say, the one in which all
the three acid hydrogen atoms are replaced by calcium — ■
has the formula Ca3(P04)2, three bivalent calcium atoms
replacing six atoms of hydrogen.

Arsenic and its Compounds. — Arsenic, As (At. Wt. 75),
occurs in nature in combination with metals, — as, for ex-
ample, iron, copper, cobalt, nickel, etc., — and in combina-
tion with oxygen as the oxide As203. It has a metallic
lustre. When heated to quite a high temperature in the
air it takes fire, and burns with a bluish flame, giving off
a smoke which has the odor of garlic and is poisonous. It

156

THE ELEMENTS OF CHEMISTBY.

combines directly with most elements. In the elementary

form it is not poisonous, but when oxidized it becomes so.

Arsine, Arseniuretted Hydrogen, AsH3. — This compound,

which in composition is analogous to ammonia, NH3, is

made by bringing a compound of arsenic with oxygen into

a mixture from which hydrogen is being evolved.

Experiment 98. — Arrange an apparatus as shown in Fig. 38.
Put some granulated zinc in the flask and pour dilute sulphuric

Fig. 38.

acid on it. When the air is all out of the vessel and the hydro-
gen is lighted, add slowly a little of a solution of arsenic oxide,
As203, in dilute hydrochloric acid. What change takes place in
the flame ? Is the color changed ? Are fumes given off ? (See
Experiment 99.)

Arsine is a colorless gas which is very poisonous and has
an unpleasant odor. When lighted it burns with a bluish-
white flame. It is very unstable, breaking up into arsenic
and hydrogen when heated. When a cold object, as a
piece of porcelain, is brought into the flame of burning
arsine, the arsenic is deposited in the form of a dark spot.

THE NITROGEN FAMILY. 157

Detection of Arsenic in Cases of Poisoning. — The con-
duct of arsine is taken advantage of for the purpose of de-
tecting the presence of arsenic. It is extensively used in
examining the stomach and other viscera of human beings
in cases of suspected poisoning. The method used is
known as Marsh's test, having been introduced by a chem-
ist by the name of Marsh.

Experiment 99. — Into the flame of the burning hydrogen and
arsine produced in the last experiment introduce a piece of por-
celain, as the bottom of a small porcelain dish or a crucible, or a
bit of a broken plate, and notice the appearance of the spots.
Heat by means of a Bunsen burner the tube through which the
gas is passing, which should be of hard glass. Just in front of
the heated place there will be deposited a thin layer of metallic
arsenic, commonly called a mirror of arsenic. This deposit is due
to the decomposition of the arsine into arsenic and hydrogen by
heat.

Arsenic Tri oxide, As203. — When arsenic is burned in the
air or oxygen it forms the trioxide. [Compare with phos-
phorus in this respect.] This substance, which is what is
commonly called arsenic, or tvhite arsenic, is made by heat-
ing compounds of arsenic and metals in contact with the
air. Under these circumstances both the metal and the
arsenic are oxidized, and the oxide of arsenic, being vola-
tile, passes off and is condensed and collected in large
chambers of mason-work. It is a colorless, glassy mass.
It is difficultly soluble in water, more easily in hydrochloric
acid. It has a weak, disagreeably sweet taste, and acts
very poisonously. It is probably more frequently used as a
poison than any other substance. Minute quantities can
be detected by the chemist with absolute certainty. It is
easily reduced by means of carbon.

Experiment 100. — Mix together about equal small quantities
of arsenic oxide and finely-powdered charcoal. Heat the mixture

158 THE ELEMENTS OF CHEMISTRY.

in a small dry tube of hard glass, closed at one end. The arsenic
which is set free will be deposited on the walls of the tube in the
form of a mirror, like that obtained in Experiment 100.

Antimony, Sb (At. Wt. 120), occurs most frequently in
combination with sulphur as the sulphide Sb2S3. It is a
silver- white, metallic-looking substance. At ordinary tem-
peratures it is not changed by contact with the air; but
when heated to a sufficiently high temperature it takes fire
and burns, forming the white oxide.

Stibine, Antimoniuretted Hydrogen, SbH3. — This com-
pound is made by the same method as that described under
Arsenic.

Experiment 101. — Make some stibine, using a solution of tar-
tar emetic, a substance which contains antimony.

Its properties are very much like those of arsine. It
burns with a similar flame, and is decomposed in the same
way.

Experiment 102. — Introduce a piece of porcelain in the flame
and notice the deposit or antimony spot. It is darker and more
smoky than the arsenic spot. There are other differences in prop-
erties, but they need not be considered here.

Boron, B (At. Wt. 10.9). — Boron may conveniently be
considered in connection with the nitrogen family, as some
of its properties suggest those of the members of that
family. At the same time, it has peculiarities which dis-
tinguish it from these elements. It occurs in nature in
the form of ioric acid, or as salts of this acid, particularly
the sodium salt, or lorax. It is prepared by treating the
oxide, B203, at a very high temperature with sodium or
aluminium. Under proper conditions it is obtained in
the form of crystals, which are almost as hard as diamonds.

Tetraboric Acid, H2B407, is the form of boric acid from

THE G ABB ON FAMILY. 159

which borax is derived. The formula of borax is Na2B407
+ 10H2O,

The Carbon Family: Carbon a^d Silicon.

Occurrence of Silicon. — Carbon, as you have seen, occurs
in every living thing. It is interesting to note that silicon,
which in some respects resembles carbon in its chemical
properties, is one of the most important constituents of the
mineral or inorganic parts of the earth. It occurs chiefly
in the form of the oxide, Si02, commonly called silica, or
silicon dioxide; and in combination with oxygen and
several of the common metals, particularly with sodium,
potassium, aluminium, and calcium, in the form of the
silicates.

Great Abundance of Silicon. — Next to oxygen silicon
occurs in largest quantity in the earth. There are exten-
sive mountain-ranges consisting almost entirely of silicon
dioxide, Si02, in the form known as quartz or quartzite.
Other ranges are made up of silicates, which are compounds
formed by a combination of silicon dioxide and bases.
The clay of valleys, river-beds, etc., also contains silicon
in large quantity, while the sand found so abundantly at
the seashore is mostly silicon dioxide, Si02.

The Element Silicon. — Unlike carbon, silicon is never
found in the uncombined state. It is an extremely difficult
thing to decompose the oxide in such a way as to get the
element. Under proper conditions silicon can be obtained
in the form of crystals which have a gray color and are
harder than glass.

Silicic Acid. — There are several varieties of silicic acid,
all of which are, however, derived from an acid of the

160 THE ELEMENTS OF CHEMISTRY.

formula ET Si(X, or normal silicic acid. When this is set
free from its salts it loses water, and is changed to ordinary
silicic acid, H2Si03:

H4SiO< = H2Si03 + H20.

When heated higher, this second form of silicic acid is con-
verted into the dioxide Si02:

H2Si03 = Si02 + H20.

Silicon Dioxide, Silicic Anhydride, Si02. — As already
stated, this substance occurs very abundantly in nature and
in many different forms. Quartz, or rock crystal, is pure
crystallized silicon dioxide; quart zite is a coarser-grained
substance made up of small crystals of quartz, usually col-
ored. Agate, amethyst, and carnelian are varieties of quartz
colored by foreign substances. Silica also occurs in the
stalks of some plants, giving them firmness, and in some
cases making them so hard that they are valuable for pol-
ishing.

Some of the more important silicates, as water-glass, glass,
and the natural silicates, will be considered farther on.

BASE-FOBMING ELEMENTS. 161

OHAPTEE XVIII.

BASE-FORMING ELEMENTS— GENERAL CONSIDERA-
TIONS.

Distinction between Acid-forming and Base-forming Ele-
ments.— The meaning of the name base-forming elements
is simply that the compounds of these elements with hy-
drogen and oxygen are bases, or, in other words, have the
power to neutralize acids and form salts. But the distinc-
tion between acid-forming and base-forming elements is
not a sharp one, for the reason that there are some elements
which form both acids and bases.

Base-forming Elements. — The base-forming elements will
be taken up in the following order:

1. The Potassium Family, the principal members of
which are potassium and sodium.

2. The Calcium Family, the principal members of
which are calcium, barium, and strontium.

3. The Magnesium Family, the principal members of
which are magnesium and zinc.

4. The Silver Family, consisting of silver, copper, and
mercury.

5. The Aluminium Family, of which aluminium is the
only well-known member.

6. The Iron Family, consisting of iron, cobalt, and
nickel.

7. The Manganese Family, of which manganese is the

only representative. There are some points of resem-
11

162 THE ELEMENTS OF CHEMISTRY.

blance between manganese and the members of the
chlorine family.

8. The Chromiu?n Family, of which chromium is the
principal member. There are some points of resemblance
between chromium and the members of the sulphur family.

9. The Bismuth Family, of which bismuth is the only
representative. Between it and the members of the nitro-
gen family there are some points of resemblance.

10. The Lead Family, the principal members of which
are lead and tin.

11. The Palladium Family, consisting of three rare
elements.

12. The Platinum Family, the principal members of
which are platinum and gold.

Large Number of Base-forming Elements. — You see that
there are many more base-forming than acid-forming
elements, and it is a serious undertaking to become
thoroughly acquainted with all the elements included
under this head. For the present it will be best to confine
our attention to a few of the most important of the ele-
ments.

Metallic Properties. — The base -forming elements are
those which are usually called metals. The name metal
is applied to those elements which have what is known as
a metallic lustre, are opaque, and are good conductors of
electricity. Gradually the name metal has come- to mean an
element which has the power to displace the hydrogen of
acids and form salts.

Classes of Metal Derivatives. — As the metals or
forming elements all combine with oxygen, sulphur,
chlorine, and also form salts with all acids, it follows that
under the head of each one there must be a large number

BASE-FORMING ELEMENTS. 1 63

of compounds. A thorough study of each metal would
include the following subjects:

1. Its Occurrence in Nature. — Under this head we
should become acquainted with those natural compounds
of the metals known as minerals. Those minerals from
which the metals are extracted for practical purposes are
called ores.

2. Extraction of the Metals from their Ores. — The study
of this subject is the object of metallurgy.

3. The Properties of Metals. — As you will find, metals
differ very markedly from one another. Some are light,
floating on water, as potassium, sodium, etc. ; some are ex-
tremely heavy, as lead, platinum, etc. Some combine
with oxygen with great energy; others form very weak
compounds with oxygen. Some form strong bases; others
form weak bases.

4. The Compounds of the Metals. — These may be con-
veniently classified as:

a. Compounds with chlorine, bromine, and iodine; or
the chlorides, bromides, and iodides.

b. Compounds with oxygen and with oxygen and hydro-
gen; or the oxides and hydroxides.

c. Compounds with sulphur and with sulphur and hy-
drogen; or the sulphides and hydrosulphides.

d. Compounds with nitric and nitrous acids; or the
nitrates and nitrites.

e. Compounds with the acids of chlorine; or the chlo-
rates, chlorites, etc.

/. Compounds with sulphuric and sulphurous acids; or
the sulphates and sulphites.

g. Compounds with carbonic acid; or the carbonates.
h. Compounds with phosphoric acid; or the phosphates.

164

THE ELEMENTS OF CHEMISTBY.

i. Compounds with silicic acid; or the silicates.

j. Compounds with boric acid; or the borates.

The acids of which the salts are derivatives are already
known to you, and in dealing with the acids frequent
reference has been made to the methods of making the
salts, and to some of their most important properties. In
what follows only those compounds will be considered
which well illustrate general principles, or which, owing
to some familiar application, happen to be of special
interest.

THE POTASSIUM FAMILY. 165

CHAPTEE XIX.

THE POTASSIUM FAMILY: POTASSIUM, SODIUM
(AMMONIUM).

Alkalies. — The members of this family are generally
called metals of the alkalies, as the two best-known mem-
bers are obtained from the alkalies, caustic potash and
caustic soda, or potassium and sodium hydroxides.

Potassium, K (At. Wt. 39). — This element is a constitu-
ent of many minerals, particularly of feldspar, which is a
silicate of aluminium and potassium.

In the Soil.— The natural decomposition of minerals con-
taining potassium gives rise to the presence of this element
in various forms of combination everywhere in the soil, and
it is of the highest importance for the plants, as they use it
as part of their food. When vegetable material is burned
the potassium remains behind, chiefly as potassium carbon-
ate. When wood-ashes is treated with water the potas-
sium carbonate dissolves, and it is obtained in an impure
state by evaporating the solution. The substance thus ob-
tained is called potash.

Experiment 103. — Treat two or three pounds of wood-ashes
with water. Filter off the solution, and examine it by means of
red litmus-paper. Is the solution alkaline ? Examine some po-
tassium carbonate. — Does its solution act in the same way ? —
Evaporate to dryness the solution obtained from the wood-ashes.
Collect the dry residue and treat it in a test-tube with a little
dilute hydrochloric acid. Is a gas given off ? Is it carbon diox-
ide ?

166 THE ELEMENTS OF CHEMISTRY.

Potassium is also found in the form of the chloride KOI,
accompanying the chloride of sodium, and as the nitrate in
saltpetre.

How Potassium is Prepared. — The metal was first pre-
pared by the action of a powerful electric current on caustic
potash, which had been considered as an element. It is
now manufactured by distilling a mixture of potassium
carbonate and charcoal:

K2C03 + 20 = 2K + 300.

Properties. — It is a light substance which floats on
water. Its freshly-cut surface has a bright metallic lustre,
almost white ; it acts upon water with great energy, caus-
ing the evolution of hydrogen, which burns, and the for-
mation of potassium hydroxide. In consequence of its
action on water, potassium cannot be kept in the air. It
is kept under some oil upon which it does not act, as pe-
troleum.

Experiment 104. — Throw a small piece of potassium not larger
than the size of a pea upon water. What takes place ? What is
the color of the flame ? What difference is there between the
action of sodium and of potassium on water ? Is the solution
after the action alkaline ? Why ?

Compounds of Potassium. — The chief compounds of po-
tassium with which we meet are the iodide, KI; the hydrox-
ide, or caustic potash, KOH; the nitrate, or saltpetre,
KN03; the chlorate, KC103; and the carbonate, K2C03.

Potassium Iodide, KI, is made by treating caustic potash
with iodine. The action is the same as that which takes
place when chlorine acts upon warm concentrated caustic
potash. Both the iodide and iodate are formed:

6K0H + 61 - 5KI + KI03 + 3H A

THE POTASSIUM FAMILY. 167

By evaporating off the water and heating the residue,

the iodate is decomposed into iodide and oxygen.

Experiment 105. — Examine a bottle of crystallized potassium
iodide. Taste a little. Dissolve some in water. Add some
iodine to this solution. Does the iodine dissolve ? Heat a little.
Does the substance contain water of crystallization ? Treat a
crystal or two with a few drops of concentrated sulphuric acid.
What takes place ? To what is the appearance of violet vapors
due ? See Experiment 87.

Potassium iodide is extensively used in medicine and in
photography.

Potassium Hydroxide, KOH. — This well-known sub-
stance, commonly called caustic potash, is prepared by heat-
ing potassium carbonate with lime (calcium hydroxide) in
a silver or iron vessel.

Experiment 106. —Dissolve 50 grams potassium carbonate in
500-600 cc. water. Heat to boiling in an iron or silver vessel,
and gradually add slaked lime made from 25 to 30 grams good
quicklime. During the operation the mass should be stirred
with an iron spatula. After the solution is cool, draw it off by
means of a glass siphon into a bottle. This may be used in ex-
periments in which caustic potash is required. The reaction is
based upon the fact that calcium carbonate is insoluble, and that
potassium carbonate and calcium hydroxide are soluble:

K2C03 + Ca02H2 = CaCOs + 2KOH.

The hydroxide is a white brittle substance. In contact
with the air it deliquesces [what does this mean-?] and ab-
sorbs carbon dioxide. It is a strong base. [What prod-
ucts are formed when it acts upon hydrochloric acid ?
Upon nitric acid ,? Upon sulphuric acid? How many
salts can it form with sulphuric acid ? What are their
formulas ?]

Potassium Nitrate, KN03 — The common name of this
salt is saltpetre. Its occurrence in nature has already been

168 THE ELEMENTS OF CHEMISTRY.

referred to. When refuse animal matter is left to un-
dergo decomposition in the presence of bases, nitrates are
formed.

Saltpetre Plantations. — Advantage is taken of the fact
just mentioned for the purpose of preparing saltpetre arti-
ficially. Heaps of refuse matter from stables are mixed
with lime and kept moist, and then allowed to stand for a
time. The nitrate which is formed is extracted with water,
converted into potassium nitrate, and purified. Places
where this process is carried on on the large scale are
called saltpetre plantations.

Properties.— Potassium nitrate crystallizes in long rhom-
bic prisms which have a salty taste. It is easily soluble in
water.

Uses of Saltpetre. — It is used in making sulphuric acid
[how?], and nitric acid [how?]. Its chief use is in the
manufacture of gunpowder.

Gunpowder. — The value of gunpowder is due to the fact
that it explodes readily, the explosion being a chemical
change accompanied by a sudden evolution of gases. When
the powder is enclosed in a gun-barrel the gases in escaping
drive the ball before them. Gunpowder has long been
known, and has always been made of saltpetre, charcoal, and
sulphur. When heated the saltpetre gives off oxygen and
nitrogen; the oxygen combines with the charcoal, forming
carbon dioxide, and the sulphur combines with the potas-
sium, forming potassium sulphide. The reactions are
represented in this equation:

2KN03 + 30 + S = 3C02 + 2N + K2S.

Gas. Gas. Solid.

Experiment 107. — Mix together 15 grams potassium nitrate
and 2.5 grams powdered charcoal. Set fire to the mass.

THE POTASSIUM FAMILY. 169

Potassium Chlorate, KC103, has so frequently been re-
ferred to and used in earlier experiments that it is not
necessary to say anything more about it now.

[Describe the method of preparation and decomposition
by heat.]

Sodium, Na {At. Wt. 23). — Sodium occurs very widely
distributed and in large quantities, principally as sodium
chloride. It occurs also as sodium nitrate, and as silicate
in many minerals. Like potassium it is found everywhere
in the soil, and is taken up by plants, especially by those
which grow in the neighborhood of the sea and in the sea.

Preparation of Sodium. — Sodium is made by the same
method as that used for making potassium.

Properties, — Its properties are very similar to those of
potassium. It is light, floating on water; it has a bright
metallic lustre, and is soft, like wax. It decomposes water,
but not as actively as potassium.

Sodium a Strong Reducing Agent. — Sodium has a strong
attraction for oxygen, and is used in some chemical pro-
cesses as a reducing agent, as, for example, in the prepara-
tion of aluminium. A compound of mercury and sodium,
known as sodium amalgam, is used in some metallurgical
operations connected with the extraction of gold and silver
from their ores.

Compounds of Sodium. — The chief compounds of sodium
are the chloride, KTaCl; the hydroxide, or caustic soda,
NaOH; the nitrate, or Chili saltpetre, NaN03; the sul-
phate, JSTa2S04; the carlonate, Na2C03; and the lor ate, or
borax, Na2B407.

Sodium Chloride, NaCl. — This is the substance known by
the name common salt. It occurs very widely distributed,
and, as it is easily soluble, much of the water which enters

170 THE ELEMENTS OF CHEMISTRY.

into the ocean contains some of it in solution. Sea-water
contains 2% to 3 per cent of sodium chloride.

How Salt is Obtained. — In some places salt is taken out
of mines in the solid form; in others water is allowed to
flow into the mines, and to remain* for some time in contact
with the salt, and the solution thus formed is drawn or
pumped out of the mine and evaporated by appropriate
methods. Salt is also obtained from the sea in hot coun-
tries. At high tide the water is dammed up, and the arti-
ficial ponds thus formed afterwards evaporate under the
influence of the sun, leaving the salt behind.

Properties. — Sodium chloride crystallizes in colorless and
transparent cubes. Sometimes that which occurs in nature
is colored blue. Its taste is familiar to every one.

Uses of Salt. — Salt is an extremely important article of
food. It appears to be necessary to the life of man as well
as of many animals. It is found in all parts of the body.
It is used to prevent decomposition of meats. Salt pork
and salt fish are familiar to all. Salt is used as the starting-
point in the preparation of all sodium compounds and of all
chlorine compounds.

[How are chlorine and hydrochloric acid obtained from
it?]

Sodium Hydroxide, NaOH. — This is commonly called
caustic soda. It can be prepared in the same way as potas-
sium hydroxide; that is, by treating a solution of sodium
carbonate with lime. [Explain the reaction.] Its prop-
erties are very similar to those of caustic potash.

Sodium Nitrate, "N"aN"Os. — This is the salt which has
been repeatedly referred to by the name of Chili saltpetre.
It occurs in very large quantities, and is the chief source of
nitric acid. It is cheaper than potassium nitrate, but can-

THE POTASSIUM FAMILY. Ill

not be substituted for it in the manufacture of gunpowder,
because it becomes moist in the air. It is converted into
potassium nitrate by treating its solution with potassium
chloride:

MaNO, + KOI = KN03 + NaOl.

Sodium Sulphate, Na2S04 + 10H2O. — The common
name of this substance is Glauber's salt. It is manufac-
tured in enormous quantities for the purpose of converting
common salt into sodium carbonate or "soda:"

2NaCl + H2S04 = 2HC1 + Na2S04.

It crystallizes in large, colorless, monoclinic prisms,
containing 10 molecules of water of crystallization,
Na2S04 + 10H2O. It loses water when left in contact with
the air.

Sodium Carbonate, Na2C03 + 10H2O. — This salt, com-
monly called soda, is one of the most important of manu-
factured chemical substances. The mere mention of the
fact that it is essential to the manufacture of glass and soap
will give an idea of its importance. It is found in the ashes
of sea-plants, just as potassium carbonate is found in the
ashes of land-plants. Formerly it was obtained from this
source. Now, however, we are not dependent upon sea-
plants for our supply, as two methods have been devised
for preparing it from sodium chloride, with which the earth
is so abundantly supplied.

Manufacture of Soda from Sodium Chloride. — During
the French Eevolution the supply of soda was cut off from
France, and the government therefore offered a large prize
for a method for making it from common salt. A method
was devised by Leblanc which has been used very exten-
sively ever since.

172 THE ELEMENTS OF CHEMISTRY.

Leblanc's Method for Making Soda. — This consists of four
reactions :

1st. The sodium chloride is converted into sodium sul-
phate by treating it with sulphuric acid :

2NaCl + H2S04 = Na2S04 + 2HC1.

2d. The sodium sulphate thus obtained is heated with
charcoal, which reduces it to sodium sulphide, ]STa2S:

Na2S04 + 40 = Na2S + 4C0.

3d. The sodium sulphide is heated with calcium carbon-
ate, when sodium carbonate and calcium sulphide are
formed :

Na2S + CaC03 = Na2C03 + OaS.

4th. If lime is present in the last reaction, it forms an
insoluble compound with calcium sulphide. By treating
the product of the reaction with water the sodium carbon-
ate alone dissolves.

In practice the sodium sulphate is mixed with charcoal
and calcium carbonate and the mixture heated.

The Solvay Method. — Another method has recently come
into great prominence, threatening to drive out the Le-
blanc method completely. This is the Solvay, or the am-
monia, method. This depends upon the fact that the salt,
HNaCOg, is comparatively difficultly soluble in water and
is therefore precipitated from a solution of common salt by
the addition of an easily soluble carbonate.*

* In 1883 there were manufactured in Germany 115,500 tons of
carbonate of soda, half of it by the Solvay method. In the same year
429,040 tons were manufactured in England by the Leblanc process*

TSE POTASSIUM FAMILY. 175

Properties.— Sodium carbonate crystallizes in large prisms
with 10 molecules of water of crystallization. The crystals
are efflorescent.

Mono-sodium Carbonate, HNaC03, or Mcarlonate of soda,
is made from sodium carbonate by passing carbon dioxide
into it:

Na2C03 + C02 + H20 = 2HNaC08.

This substance is one of the constituents of laking-pow-
ders which are used for raising bread. Roclielle powders con-
sist of the bicarbonate and cream of tartar mixed together.
When water is added to the mixture, carbon dioxide is
given off, as the cream of tartar is an acid salt, acid potas-
sium tartrate, KH5C406, and Roclielle salt is left in solu-
tion. This is the potassium and sodium salt of tartaric
acid, of the composition ENaH4C406. [Why are such
salts called double salts?]

Disodium Phosphate, Na2HP04 + 12H20.— This is the
common form of sodium phosphate.

Sodium Borate, Borax, ¥a2B407 + 10H2O. — This salt is
found in several lakes in Asia, and in this country in Clear
Lake, Nevada. It is also manufactured by neutralizing the
boric acid found in Tuscany. When heated, borax puffs
up, and at red heat melts, forming a transparent, colorless
liquid. This is the dry substance, Na2B407. Molten borax
has the power to dissolve the oxides of the metals, and
forms colored glasses with some of them. In soldering
it is necessary that the metals should be clean and bright.
To secure this a little molten borax is put on the surfaces
which are to be united. Borax is an antiseptic; that is to
say, it prevents the decomposition of organic subtances.

174 THE ELEMENTS OF CHEMISTRY.

Water-glass. — Silicon dioxide, or silica, Si02, dissolves
by continued boiling with caustic soda or potash, and so-
dium or potassium silicate is thus formed:

Si02 + 2NaOH = Na2Si03 + H20.

These salts are soluble in water, and are known as water-
glass. Water-glass is used in making artificial stone, and
for the purpose of protecting certain stones from the action
of the weather.

Ammonium Salts. — When the gas ammonia, NHS, or its
solution in water, is brought together with acids, salts are
formed. Thus ammonia and hydrochloric acid give a salt
of the composition NH4C1; ammonia and nitric acid give
NH4N03; ammonia and sulphuric acid give (NH4)2S04.
These salts are formed according to the following equations:

NH3 +H01 =NH401;
NH3 + HN03 = NH4NOa;
2NH3 + H2S04 = (NHJ2S04.

The salts thus formed are much like the salts of sodium
and potassium. The only way to compare them with the
salts of the metallic elements is by assuming that in them
the part represented by NH4 acts the part of the metal.
It is called ammonium, and the salts are called ammonium
salts. Ammonium has never been obtained in the uncom-
bined state, as instead of it ammonia is always formed.

Experiment 108. — Place near each other two vessels, one con-
taining a little strong hydrochloric acid, and the other a little
strong ammonia. Explain what you see.

Ammonium Chloride, OT34C1. — This salt is commonly
called sal-ammoniac* At present its principal source is

THE POTASSIUM FAMILY. 175

the gas-works. When heated it is converted into vapor
without melting, and with very slight decomposition.

Experiment 109. — On a piece of platinum-foil or porcelain
heat a little ammonium chloride. What is the result ?

[What takes place when ammonium chloride is treated
with caustic soda? With lime?]

Ammonium Sulphide, (NH4)2S. — This salt, which is made
by treating ammonia with hydrogen sulphide, is extensively
used in making chemical analyses.

Relations between the Atomic Weights of the Alkali
Metals. — The atomic weight of lithium, which is a metal
belonging to the potassium family, is 7. Between this and
the atomic weights of sodium, 23, and potassium, 39, ex-
ist relations similar to those which exist between the atomic
weights of chlorine, bromine, and iodine; and of sulphur,
selenium, and tellurium. [What is this relation?]

Flame Reactions. — When a piece of clean platinum wire
is held for some time in the flame of the Bunsen burner, it
then imparts no color to the flame. If now a small piece
of sodium carbonate or any other salt of sodium be put in
it, the flame is colored intensely yellow. AH sodium com-
pounds have this power, and hence the chemist makes use
of the fact for the purpose of detecting the presence of
sodium. Similarly, potassium compounds color the flame
violet.

Experiment 110. — Prepare some pieces of platinum wire, 8 to
10 cm. long, with a small loop on the end. After thoroughly
cleaning them, insert one in a little sodium carbonate, and notice
the color it gives to the flame. Try another with potassium car-
bonate.

To Separate Two or More Colors. — While it is an easy
matter to recognize potassium alone, or sodium alone, it is

176 THE ELEMENTS OE CHEMISTRY.

not so easy to do so when they are together in the same
compound. The intense yellow caused by the sodium com-
pletely masks the more delicate violet caused by the potas-
sium, so that the latter cannot be seen by the unaided eye.
In this particular case we can get over the difficulty by let-
ting the light pass through a blue glass, or a thin vessel
filled with a solution of indigo. The yellow light is thus
cut off, while the violet light passes through and can be
recognized.

The Prism and the Spectrum. — A better method for de-
tecting what a light is made of is by means of a prism.
Lights of different colors are turned out of their course
to different extents when passed through a prism, as is
seen in the case of sunlight. A narrow beam of white
light passing in emerges as a band of various colors, called
its spectrum. It is thus seen that white light is made of
different-colored lights. Similarly, we can determine what
any light is composed of. Every light has its characteris-
tic spectrum. The light produced by burning sodium, or
by introducing a sodium compound in a colorless flame,
has a spectrum consisting of a narrow yellow band. The
spectrum of potassium consists mainly of two bands, one
red and one violet. Further, these bands always occupy
definite positions relatively to one another, so that, in
looking through a prism at the light caused by potassium
and sodium, the yellow band of sodium is seen in its posi-
tion, and the two potassium bands in their positions.

The Spectroscope. — The instrument used for the purpose
of examining the spectra of different lights is called the
spectroscope. It consists essentially of a prism and two
tubes. Through one of the tubes the light to be examined
is allowed to pass so as to strike on the prism. The light

THE POTASSIUM FAMILY, 177

emerges from the other side of the prism, and is observed
through the other tube, which is provided with lenses for
the purpose of magnifying the spectrum. By means of
the spectroscope it is possible to detect the minutest quan-
tities of some elements, and, since it was devised, several
new elements have been discovered through its aid, as, for
example, caesium, rubidium, thallium, indium, and gallium.
12

178 THE ELEMENTS OF CHEMISTRY.

CHAPTEE XX.

THE CALCIUM FAMILY: CALCIUM, BARIUM,
STRONTIUM.

Calcium, Ca {At. Wt. 40). — This is the principal mem-
ber of the family. It is widely distributed in nature and
in enormous quantities; principally as carbonate, CaC03,
in the form of limestone, marble, and chalk; as sulphate,
CaS04, in the form of gypsum ; as phosphate, Oas (P04)2,
in phosphorite and apatite; as fluoride, CaF2, in fluor-spar.

The element is not easily made. It acts upon water just
as sodium and potassium do.

Compounds of Calcium. — The principal compounds of
calcium with which we have to deal are the chloride, CaCl2;
the oxide, or quicklime, CaO; the hydroxide, or slaked
lime, Ca02H2; the hypochlorite, Ca(001)2; the carbonate,
Ca003; the sulphate, CaS04; the phosphate, Oa3(P04)2;
and the silicates, in the form of glass.

Calcium Chloride, Ca012. — The property which gives
this salt its value is its power to absorb water. It is used
as a drying agent. Gases are passed through it for the
purpose of drying them, and it is also placed in vessels in
which it is necessary that the atmosphere should be kept
dry.

Experiment 111. — Dissolve 10 to 20 grams of limestone or
marble in ordinary hydrochloric acid. Evaporate to dryness.
Expose a few pieces of the residue to the air. — Does it become
moist? In what experiments has calcium chloride been used,

THE CALCIUM FAMILY, 179

and for what purposes ? What would happen if sulphuric acid
were added to calcium chloride? Try it. Explain what takes
place. Is the residue soluble or insoluble in water ?

Calcium Oxide, CaO. — This is the substance commonly
called lime. It is made by heating calcium carbonate,
which is decomposed into lime and carbon dioxide:

CaC03 = CaO + C02.

Limekilns are large furnaces in which limestone and
other forms of calcium carbonate are heated and converted
into lime.

Lime is a white substance which does not melt. When
heated in the flame of the compound blow-pipe, it gives
forth an intense light, as any other infusible substance
would under the same circumstances. When exposed to
the air, it attracts moisture and carbon dioxide,, and is
thus converted into the carbonate. This change is called
air-slaking, and lime thus changed is said to be air-
slaked.

Calcium Hydroxide, Ca02H2. — When calcium oxide or
quicklime is treated with water it becomes hot and crum-
bles to a fine powder. The substance which is formed in
this operation is somewhat soluble in water, the solution
being known as lime-zvater.

Slaking. — The action which takes place when lime is
treated with water is called slaking. It is represented by
the equation

CaO + H20 = CaOaH2.

The oxide is converted into the hydroxide or hydrate.

Experiment 112. — To 40 or 50 grams good quicklime add
100 cc. water. What takes place ? Afterwards dilute to 2 to 3

180 THE ELEMENTS OF CHEMISTRY,

litres and put the whole in a wide-stoppered bottle. The un-
dissolved lime will settle to the bottom, and in the course ot
some hours the solution above will become clear. Carefully pour
off some of the clear solution. What takes place when some of
the solution is exposed to the air? When the gases from the
lungs are passed through it ? When carbon dioxide is passed
through it? What takes place when dilute sulphuric acid is
added to lime-water? Is calcium sulphate difficultly or easily
soluble in water ? Has lime-water an alkaline reaction ? What
reaction would you expect to take place between lime and nitric
acid?

Calcium Hypochlorite, Ca(OCl)2, has already been treated
of sufficiently under the head of Chlorine. It need only
be repeated that the form in which chlorine is transported
is " Meacliing-powder" or "chloride of lime" This is a
compound containing calcium hypochlorite and calcium
chloride, 0a(0Cl)2 + CaCl2, which is made by passing chlo-
rine into slaked lime*

20a(OH)2 + 4C1 = Ca(OCl)2 + CaCl2 + 2H20.

v v '

Bleaching-p o wder .

How Bleaching-powder Gives up Chlorine. — Bleaching-
powder gives up its chlorine by simple exposure to the air
in consequence of the action of the carbon dioxide. The
addition of an acid causes a rapid evolution of chlorine.

Calcium Carbonate, CaC03. — This salt occurs in nature in
the well-known forms calc-spar, limestone, marble, and
chalk. The variety of calc-spar found in Iceland, and
known as Iceland spar, is particularly pure calcium carbon-
ate. The salt also forms the principal part of oyster-shells,
coral, etc. In some caves water containing calcium car-
bonate in solution drips down, and the salt is deposited in
the solid form from the solution. Thus there are formed

THE CALCIUM FAMILY, 181

hanging pieces, shaped like icicles, and below them reach-
ing up from the bottom are similar pieces with the pointed
ends upwards. Those which hang down from above are
called stalactites, those on the bottom are called stalagmites.

Calcium Sulphate, Gypsum, CaS04 + 2H70. — Gypsum is
the principal variety of calcium sulphate. When heated
it loses its water of crystallization and forms a powder
called plaster of Paris, which has the power of taking up
water and forming a solid substance. The process of solid-
ification is known as " setting. v Plaster of Paris is largely
used in making casts.

Permanent Hardness of Water. — Calcium sulphate is
somewhat soluble in water A natural water containing it
is called a hard water, just as is water which contains cal-
cium carbonate. The haMness caused by calcium carbon-
ate is remedied by boiling the water, and is, therefore,
called temporary hardness, while that which is caused by
gypsum is not remedied by boiling and is therefore called
permanent hardixess. Why the water is called hard will be
explained when the subject of soap is treated.

How to Improve Hard Water. — Water which holds cal-
cium carbonate in solution can be made soft by adding a
little lime to it. This forms insoluble calcium carbonate
with the carbon dioxide, and, as soon as the carbon di-
oxide is removed, the calcium carbonate which is in solu*
tion is precipitated. If the hardness is caused by calcium
sulphate the addition of a little carbonate of soda will pre-
cipitate the calcium as calcium carbonate, and sodium sul-
phate will be left in solution:

CaS04 + Na2C03 = CaCO, + Na2S04.
[Try these reactions.]

182 THE ELEMENTS OF CHEMISTRY.

Gypsum Valuable as a Fertilizer. — The addition of

gypsum to a soil increases its fertility, and it is therefore

frequently used by farmers to increase their crops.

Experiment 113. — Heat some powdered gypsum to about 200°
in an air-bath. Examine what is left and see whether it will be-
come solid when mixed with a little water so as to form a paste.
See whether gypsum itself will act in the same way.

Calcium Phosphate, Ca3(P04)2. — The normal phosphate
in which all the hydrogen of phosphoric acid is replaced
by calcium is found in nature as phosphorite, and in com-
bination with calcium fluoride or chloride as apatite. Fur-
ther, it is the chief earthy constituent of bones, and is
found in large quantity in bone-ash.

Calcium Phosphate as a Fertilizer. — Plants need phos-
phoric acid for their growth, and hence it must be present
in the soil if the plants are to flourish. Ordinary normal
calcium phosphate is not soluble, and is therefore not easily
taken up by the plants. It can be rendered soluble by
adding sulphuric acid to it, and then it is readily used by
the plants.

Superphosphate of Lime. — Normal calcium phosphate
which has been treated with a certain proportion of sul-
phuric acid forms the valuable artificial fertilizer known as
superphosphate of lime. This is a mixture of the phos-
phate Ca (H2P04)2 and calcium phosphate formed thus*

Oa,(P04)1+2HJS04 = 20aS04 + Ca(H2P04)2.

Superphosphate of lime.

Mortar. — Mortar is made of slaked lime and sand.
When this mixture is exposed to the air, carbonate of cal-
cium is slowly formed, and the mass becomes extremely
harb. The water contained in the mortar soon passes oil.

THE CALCIUM FAMILY. 183

but nevertheless freshly-plastered rooms remain moist for
a considerable length of time. This is due to the fact that
a reaction is constantly taking place between the carbon
dioxide and calcium hydroxide in which calcium carbonate
and water are formed,

Ca02H2 + CO. = CaC03 + H30,

and it is the water thus set free which keeps the air moist.
The complete conversion of the lime into carbonate re-
quires a very long time, because the carbonate which is
formed on the surface tends to protect the lime in the in-
terior. The hardening may be promoted by keeping up
fires of coke or charcoal and allowing the product of com-
bustion to escape into the rooms.

Glass. — Common glass is a silicate of calcium and so-
dium, made by melting together sand (silicon dioxide,
Si02) with lime, or calcium carbonate, and sodium carbon-
ate. When potassium carbonate is used instead of sodium
carbonate the glass is more difficultly fusible. Bohemian
glass, which is so extensively used in the manufacture of
chemical apparatus, is a silicate of calcium and potassium.
Flint-glass } which is especially valuable for the manufac-
ture of optical instruments, contains lead instead of cal-
cium It melts much more readily than calcium glass.

Colored Glass. — Colors are given to glass by putting in
the fused mass small quantities of various substances.
Thus a cobalt compound makes glass blue; copper and
chromium make it green; one of the oxides of copper
makes it red, etc.

Compounds of Barium and Strontium. — These closely re-
semble those of calcium, Barium forms an oxide, BaOj

184 THE ELEMENTS OF CHEMISTRY.

corresponding to lime, and also another one known as ba*
rium dioxide, Ba02. This is formed by passing oxygen
or air over barium oxide heated to a dull red heat. At a
higher temperature it gives off the oxygen. These facts
have recently been taken advantage of for the purpose of
extracting oxygen from the air.

Barium Dioxide Used in Making Hydrogen Dioxide. —
Barium dioxide has already been referred to in describing
the preparation of hydrogen dioxide, H202. When it is
treated with sulphuric acid this reaction takes place:

Ba02 + H2S04 = H202 + BaS04.

When it is treated with hydrochloric acid hydrogen di-
oxide is also formed, thus:

Ba02 -f 2HC1 = H202 + BaCl2.

[Compare this with the reaction which takes place when
hydrochloric acid acts upon manganese dioxide.]

Flame Reactions. — Calcium compounds color the flame
reddish yellow; strontium compounds, intense red; and
barium compounds, yellowish green. They are frequently
used for the purpose of producing colored lights.

Relations between the Atomic Weights. — The atomic
weight of calcium is 40, that of strontium 87.5, and that
of barium 137. [Why is this fact of special interest?]

THE MAGNESIUM FAMILY. 185

CHAPTER XXI.

THE MAGNESIUM FAMILY: MAGNESIUM, ZINC,
CADMIUM,

THE COPPER FAMILY: COPPER, MERCURY, SILVER.

Magnesium, Mg {At. Wt. 24). — Magnesium occurs very
widely distributed in nature, and in considerable quantities.
Among the important magnesium minerals are magnesite,
which is the carbonate, MgC03; dolomite, a carbonate of
magnesium and calcium; soapstone, serpentine, and meer-
schaum, which is essentially a silicate of magnesium.
Further, there are many well-known minerals which contain
magnesium, as asbestos and hornblende. The element is
also found in solution in many spring- waters in the form of
the sulphate, which is known as Epsom salt.

Preparation of Magnesium.— It is prepared by treating
magnesium chloride with sodium at a high temperature.

Properties. — It is a silver- white metal with a high lustre.
In the air it changes slowly, but it gradually becomes coy
ered with a layer of the oxide. It burns with a bright
flame, forming the white oxide. At ordinary temperatures
magnesium does not decompose water; at 100° it decom-
poses it slowly. [Compare magnesium with potassium and
sodium in this respect.]

Magnesium Oxide, MgO. — This compound is commonly
called magnesia. A fine white variety is made by heating
precipitated magnesium carbonate; this is called magnesia

186 THE ELEMENTS OF CHEMISTRY.

usta. It is very difficultly soluble in water, forming with
it magnesium hydroxide, Mg02H2, which is practically in-
soluble in water. [What difference is there between mag-
nesium and calcium in this respect?]

Zinc, Zn {At. Wt. 65). — Zinc occurs in nature in combi-
nation as the carbonate, or calamine, ZnC03, as the silicate,
and as the sulphide, or zinc blende, ZnS.

Preparation of Zinc. — It is prepared by mixing the oxide
with charcoal and heating in earthenware retorts. The
metal, being volatile, passes over and is condensed.

Properties of Zinc. — Zinc has very different properties at
different temperatures. At ordinary temperatures it is
quite brittle; at 100-150° it can be rolled out in sheets, but
above 200° it becomes brittle again. In dry air it does not
change. When heated in the air it takes fire, and burns
with a bluish flame, forming zinc oxide. It dissolves in all
the common acids, usually with an escape of hydrogen.

Uses. — It is used very largely in making batteries. Iron
covered with a layer of zinc is known as galvanized iron.
Zinc is one of the constituents of brass, the other being
copper. German silver consists of brass to which some
nickel has been added.

Zinc Oxide, ZnO, is obtained as Flores zmci by burning
zinc, and by heating the carbonate or nitrate of zinc. It
turns yellow when heated, but becomes white again on
cooling.

Experiment 114. — In a furnace, or in a hot stove fire, heat a
small sand crucible to a bright red heat. Throw into it pieces of
zinc. If the temperature is high enough the zinc will boil and
the vapor will burn with a bright light, and dense white fumes of
the oxide will be formed.

Zinc oxide is used as a constituent of paint under the

THE COPPER FAMILY. 187

name zinc-white. Lead- white turns black quite readily.
Zinc-white does not.

Zinc Sulphate, ZnS04 + 7H20. — The common name of
this salt is tuhite vitriol. It is obtained on the large scale
by heating zinc sulphide in contact with the air. Under
these circumstances the sulphide is oxidized:

ZnS + 40 = ZnS04.

This operation is known as roasting. By roasting zinc
sulphide at a higher temperature it is converted into zinc
oxide:

ZnS + 30 = ZnO + S02.

Zinc sulphate is also formed in large quantities in gal-
vanic batteries and in the preparation of hydrogen.

Copper, Cu (At. Wt. 63.2). — Copper occurs in nature in
the uncombined or native state in large quantities in the
neighborhood of Lake Superior, United States, and in
Chili. It also occurs in combination with oxygen as ruby
copper, which is the oxide, Cu20; and with sulphur and
iron in copper pyrites.

Preparation of Copper. — Copper is obtained from the
oxide by heating it with charcoal. [This reduction has
been illustrated under the head of carbon (see Experiment
70).] It is also obtained from the sulphides. The chemi-
cal changes involved are comparatively complicated.

Properties.— Copper is a hard metal of a reddish color
and metallic lustre. In dry air it does not change, but in
moist air it gradually becomes covered with a green layer
of a carbonate of copper. Mtric acid dissolves it, copper
nitrate, Cu(N03)2, being formed, and oxides of nitrogen

188 THE ELEMENTS OF CHEMISTRY.

evolved [explain the reaction] ; hydrochloric acid does not
act upon it; sulphuric acid acts when heated with the
metal; the sulphate, CuS04, is formed and sulphur dioxide
given off [explain the reaction]. Copper cannot decom-
pose water, even when water vapor is passed over the metal
heated to red heat. [Compare with the conduct of the
members of the potassium, calcium, and magnesium fami-
lies.]

Copper-plating. — Copper is precipitated from solutions of
its salts by zinc, iron, and some other metals, and by an
electric current.

Experiment 115. — Into a neutral solution of copper sulphate
insert a strip of zinc. The zinc will become covered with a layer
of copper, and zinc will pass into solution as zinc sulphate. The
zinc simply displaces the copper in this case, as it displaces hy-
drogen frcm sulphuric acid:

Zn + CuS04 = ZnS04 + Cu;
Zn + H2S04 = ZnS04 4- H2.

Perform a similar experiment, using a strip of sheet-iron in-
stead of zinc. [What is the result ?]

The deposition of metallic copper from solutions of its
salts is extensively used in copper-plating. The object to
be covered with copper is hung in a solution of copper sul-
phate and connected with one pole of a galvanic battery,
the other pole being also in the solution. Decomposition
takes place, and a layer of copper is deposited on the ob-
ject.

Alloys of Copper. — Mixtures of metals made by melting
them together are called alloys. Brass is an alloy consist-
ing of about 1 part of zinc and 2 parts of copper. Bell-
metal and Ironze are alloys of copper and tin.

Copper Forms Two Series of Salts. — Copper has the power

THE COPPEB FAMILY 189

to form two distinct series of compounds,, of which the
following are examples:

CuCl, Cu012;
CuBr, CuBr,;
Cu20, CuO.

Those which belong to the first class, corresponding to the
chloride, CuCl, are called cuprous compounds. Thus,
CuOl is cuprous chloride; Cu20, cuprous oxide, etc. On
the other hand, compounds of the second class are called
cupric compounds. Thus, CuCla is cupric chloride; CuO,
cupric oxide, etc. Mercury, iron, and some other metals
also form two series of compounds whhh differ from each
other in much the same way.

Cuprous Oxide, Cu20, is found in nature as ruby copper,
and is formed when copper is heated in contact with the
air. It is a bright-red, insoluble compound.

Cupric Oxide. CuO, is obtained by heating copjoer to
redness in contact with the air, or by heating the nitrate.
It is also formed when caustic soda or potash is added to a
boiling-hot solution of a copper salt. If the solution is
cold, blue cupric hydroxide, Cu02H2, is precipitated, bui
this easily loses water, particularly if the solution is heated.
The reactions which take place are:

CuS04 + 2N"aOH = Cu02H2 + Na2S04, and
Cu02H2 = CuO + H20.

Experiment 116. — Add some caustic soda or potash to a small
quantity of a cold solution of copper sulphate in a test-tube.
After noticing the appearance of the precipitate first formed, neat.
What change takes place ?

190 TEE ELEMENTS OF CEEMISTBY.

Copper Sulphate, CuS04 + 5H20. — This salt is manu-
factured on a large scale,, and is commonly known by the
name " blue vitriol." [What salt is called " white vitriol"?]
It forms large blue crystals, which, when heated, lose water
and become colorless. The colorless substance becomes
blue again in contact with water.

Mercury, Hg (At. Wt. 200). — Mercury occurs in the un-
combined state as drops enclosed in rocks, though princi-
pally in combination with sulphur as cinnabar, HgS. It
is obtained by roasting cinnabar, when vapors of mercury
and sulphur dioxide are given off. The mercury is then
condensed in appropriate vessels. It is a silver- white metal
of a high lustre. At ordinary temperatures it is liquid,
though it becomes solid at — 39°. 5. It does not change in
the air at ordinary temperatures. It is insoluble in hydro-
chloric acid and cold sulphuric acid. [Try each.] It dis-
solves in hot concentrated sulphuric acid, and is easily
soluble in nitric acid. [Try each.] The vapor of mercury
is very poisonous.

Amalgams. — With other metals mercury forms alloys
called amalgams. In ordinary galvanic batteries the zinc
plates are treated with mercury, and thus covered with a
layer of zinc amalgam which protects them from the action
of the acids used.

Mercuric Oxide, HgO, is the red substance which was
used in one of the first experiments for the purpose of pre-
paring oxygen. It is formed when mercury is heated for
some time near its boiling-point in contact with the air,
and is made by heating the nitrate.

Mercurous Chloride, HgCl, is commonly known by the
name calomel. It is precipitated when a soluble chloride
or hydrochloric acid is added to a solution of any mercu-

THE COPPER FAMILY. 191

rous salt. It is manufactured by subliming an intimate
mixture of mercuric chloride and mercury:

HgCl, + Hg - 2HgCl.

It is a white substance,, insoluble in water, which finds ex-
tensive application in medicine.

Mercuric Chloride, HgCl2, commonly called corrosive svb-
hmate, is manufactured on the large scale by subliming an
intimate mixture of mercuric sulphate and common salt:

HgS04 + 2Na01 = Na2S04 + HgCl2.

It is a white substance, soluble in water. It is extremely
poisonous, and prevents the decay of organic substances.

Silver, Ag (At Wt. 108). — Silver occurs in the uncom-
bined state or native; in combination with sulphur; and
with sulphur and other metals. Small quantities of silver
sulphide are found in almost all varieties of galenite or
lead sulphide. It occurs more rarely as the chloride,
bromide, and iodide.

Extraction of Silver from its Ores.— Much of the silver
used is obtained from galenite. This mineral is treated in
such a way as to effect the separation of the lead (see
Lead), and the silver is separated from sulphur at the
same time. But it is dissolved in a large quantity of lead,
and the problem which presents itself to the metallurgist
is how to separate the small quantity of silver from the
large quantity of lead.

PattisorCs Process. — The separation of the silver from
the lead is accomplished by a process invented by Pattison.
It consists in melting the mixture and allowing it to cool

192 THE ELEMENTS OF CHEMISTRY.

until crystals appear, These are nearly pure lead. They
are dipped out and the liquid left is again treated in the
same way. By this means there is finally obtained a pro-
duct which is rich in silver, but which still contains some
lead. This is heated in appropriate vessels in contact with
the air, when the lead is oxidized, while the silver remains
in the metallic state. This last process is called cupellation.
Amalgamation Process. — Some ores of silver are treated
in another way, known as the amalgamation process. The
ores are mixed with common salt and roasted, when the
silver is obtained in the form of the chloride. The mass
is then treated with iron and water, when this reaction
takes place:

2A.g01 + Fe = Fe012 + 2Ag.

The mass is next treated with mercury, which forms an
amalgam with the silver. When this amalgam is taken
out, dried and heated, the mercury passes over, while the
silver remains behind.

Properties of Silver. — Silver is a white metal with a
high lustre. It is not acted upon by air, oxygen, or water
at ordinary temperatures. Sulphur acts readily upon it,
causing it to blacken superficially, the black coating being
silver sulphide. Silver coins and other articles carried in
the pockets are apt to become tarnished in consequence of
the presence of small quantities of sulphur in the perspi-
ration.

Alloys of Silver. — The silver which is used for coins and
most other purposes is an alloy with copper, the pure
metal being too soft. The alloy usually contains from 7-J
to 10 per cent of copper.

Silver-plating. — Objects are covered with silver mostly

THE COPPER FAMILY. 193

by connecting them with one pole of an electric battery
and placing them in a bath containing a silver salt in solu-
tion, in which the other pole of the battery is also inserted.
Glass is covered with silver by putting it into a solution
containing silver together with something which has the
power to separate the silver in the metallic state when
heated. Under these circumstances the silver is deposited
in a smooth, lustrous layer. Mirrors are made in this
way.

Silver Nitrate, AgN"03, is known also by the name
" lunar caustic/' as it has the power to destroy the flesh,
and is therefore used to burn out wounds. It is prepared
by dissolving silver in dilute nitric acid. Marks made by
silver nitrate turn black in the sunlight. Hence this salt
is used as a constituent of indelible inks. When working
with silver salts the fingers are apt to become stained.
These stains and generally any spots made by silver salts
can be removed by a solution of potassium cyanide, which
forms soluble salts with compounds of silver.*

Experiment 117. — Dissolve a ten or twenty-five cent piece in
dilute nitric acid. What action takes place ? Dilute the solu-
tion to 200 to 300 cc. with water. What is the color of the solu-
tion ? What does this indicate ? Does this color prove the
presence of copper ? Add a solution of common salt until it
ceases to produce a precipitate. The chemical change which
takes place is expressed by the equation

AgN03 + NaCl = AgCl + NaNO..

Insoluble.

* Quite recently some scoundrel disfigured the beautiful marble
statue of the great chemist Liebig which is in Munich by bespatter-
ing it with a solution of nitrate of silver. The professors of chem-
istry in the university succeeded, however, in removing the stains
completely by applying a paste containing potassium cyanide.
13 "

194 THE ELEMENTS OF CHEMISTRY.

The copper nitrate is not changed and remains in solution.
Filter off the white silver chloride and carefully wash with hot
water. Dry the precipitate on the filter, by placing the funnel with
the filter and precipitate in an air-bath heated to about 110°.
Remove the precipitate from the filter and put it into a porcelain
crucible. Heat gently with a small flame until the chloride is
melted. Cut out a piece of sheet-zinc large enough to cover the
silver chloride. Lay it on the silver chloride. Now add a little
water and a few drops of dilute sulphuric acid, and let the whole
stand for twenty -four hours. The silver chloride is changed to
silver, and zinc chloride is formed:

Zn + 2AgCl = ZnCl2 -h 2Ag.

Take out the piece of zince and wash the silver with a little
dilute sulphuric acid, and then with water. Dissolve the silver
in dilute nitric acid and evaporate to dryness on the water-bath,
so that the excess of nitric acid is driven off. Dissolve the resi-
due in water, and put the solution either in a bottle of dark glass
or one wrapped in dark paper.

Experiment 118. — To a few cubic centimetres of water in a
test-tube add 5 to 10 drops of the solution of silver nitrate just
prepared. To this dilute solution add a little of a dilute solution
of sodium chloride. What takes place ? Place it aside where the
light can shine upon it, and notice the change of color which
gradually takes place. In the same way make the bromide by
adding potassium bromide, and the iodide by adding potassium
iodide to silver nitrate.

Photography. — The last experiments showed that the
chloride, bromide, and iodide of silver are insoluble in
water and are changed by light. The art of photography
is based upon the changes which certain compounds, es-
pecially salts of silver, undergo when exposed to the light.
A plate of glass is covered with a thin layer of a salt of
silver. The plate is then exposed in the camera to the
action of the light from the object to be photographed.
Where the light acts upon the salt it is changed, while

THE COPPER FAMILY. 195

where the light does not act it is not changed. An image
of the object towards which the plate was directed is thus
left on the plate. The image must be developed by treat-
ing the plate with a solution of gallic or pyrogallic acid,
or a solution of ferrous sulphate. After the image is de-
veloped, the plate is treated with something which dis-
solves the unchanged silver salt. The best substance for
this purpose is a solution of sodium hyposulphite.

196 THE ELEMENTS OF CHEMISTRY.

OHAPTEE XXII.

THE ALUMINIUM FAMILY— THE IRON FAMILY: IRON,
COBALT, NICKEL.

Aluminium, Al (At. Wt. 27). — Aluminium is the only
element of the family which it represents which need be
considered here. It is an extremely important element
which occurs very widely distributed in nature. Among
the many important and widely-distributed minerals which
contain aluminium are feldspar, granite, mica, and cryolite.
Clay is essentially a silicate of aluminium.

Preparation of Aluminium. — Aluminium is prepared by
treating the chloride with metallic sodium. [How is mag-
nesium prepared ? How sodium ?] Quite recently a meth-
od has been devised by which it appears to be possible to
make aluminium much more cheaply than it has been
made hitherto. The new method consists in mixing the
oxide of aluminium with carbon and passing the current
from a powerful electrical machine through the mixture.
The apparatus is known as the Oowles electric furnace.

Properties. — Aluminium has a strong lustre; its color is
like that of tin. It is very strong and yet malleable. It
is lighter than most metals in common use, its specific
gravity being 2.7, while that of iron is 7.8, that of silver
10.57, and that of tin 7.3. Further, it does not change

liver
•e in

TEE ALUMINIUM FAMILY. 197

dry or moist air. These properties give it great value, and
it is only the fact that it cannot be prepared sufficiently
cheaply from the compounds of aluminium found in
nature that prevents its wide-spread use. It appears
probable that in the course of time aluminium will largely
take the place of iron, as it is certainly better adapted to
most of the uses to which iron is put.

Aluminium Oxide, A1203. — This compound occurs rarely
in nature in the form of ruby, sapphire, and corundum.
It is very hard, and as emery, which is powdered corun-
dum, is used for polishing. It is made artificially by
heating the hydroxide, A103H3:

2A103H3 = Ala03 + 3H,0.

Alums. — Aluminium sulphate forms complex compounds
with the sulphates of the alkali metals, all of which crys-
tallize beautifully. Potassium alum is the best known of
these. It may be regarded as derived from 2 molecules of
sulphuric acid, 2H2S04 = H4S208, by the replacement of 3
atoms of hydrogen by 1 atom of aluminium, and the fourth
by 1 atom of potassium; thus, A1KS908 or A1K(S04)2. The
crystals always contain 12 molecules of water, the complete
formula being A1K(S04)2 -f 12H20. Similarly, sodium
alum is AlKa(S04)2 + 1^H20, and ammonium alum,
A1NH4(S04)2 + 12H20.

Uses of Alum. — Alum and other compounds are used in
dyeing cotton cloth. Colors do not adhere to cotton fibre
as they do to wool and silk. On adding aluminium hy-
droxide or alum to the cotton the dye-stuffs unite with
these and form insoluble compounds. Substances which

198 THE ELEMENTS OF CHEMISTRY.

have the power of combining with dye-stuffs in this way
are called mordants. Alum is an acid salt and has the
power of decomposing carbonates. It is therefore some-
times wrongly used as a constituent of "baking powders"
in connection with sodium bicarbonate.

Aluminium Silicates. — The silicate of aluminium occurs
in nature in enormous quantities, in combination with
other silicates forming some of the most important min-
erals. The most abundant of these is ordinary feldspar y
AlKSi308. When these silicates are subjected to the influ-
ence of the air, rain, frost, etc., they suffer decomposition.
The silicate of the alkali metal dissolves and is washed
away, while aluminium silicate is partly Jeft behind and is
also partly washed away. Pure aluminium silicate is
known as kaoline, and has the composition Al4(Si04)3 +
4H20. The impure varieties are called clay.

Porcelain, etc. — Kaoline is used for making porcelain.
For this purpose it is mixed with water and moulded into
the proper shape and then heated to a high temperature
in a properly-constructed furnace. The ordinary varieties
of clay are used for making common earthenware vessels
and bricks. Earthenware and porcelain are glazed in two
ways: porcelain by coating it with an easily-fusible sub-
stance and heating to a high temperature; earthenware by
heating to a strong red heat in a furnace and throwing in
a quantity of damp salt. The salt is decomposed and
sodium silicate is formed. This fuses on the surface of
the vessels and forms a layer which is not porous.

Ultramarine. — The substance known as lapis lazuli con-
sists of a silicate of aluminium and sodium, together with
a sulphide of sodium, The coloring-matter obtained by

THE IBON FAMILY. 199

powdering it was formerly expensive, "but it is now made
artificially by the ton, and the color of the artificially -pre-
pared substance is even more beautiful than that of the
natural. It is made by heating a mixture of clay, dry
sodium carbonate, sulphur, and wood-ashes without access
of air.

Aluminium Bronze. — This is an alloy of aluminium and
copper, containing 10-12 per cent of the former. It is ex-
tremely hard and very durable, and has many useful appli-
cations. Its color is similar to that of gold.

Iron, Fe (At. Wt. 56). — At the present time it is un-
doubtedly true that iron is the most important metal for
man. It occurs in the form of magnetite, Fe304, and hem-
atite, Fe203; as the carbonate, or siderite, FeC03; in
combination with sulphur as iron pyrites, FeS2; and as
silicates and hydrated oxides, or hydroxides. Iron in the
metallic state is found in the form of meteors or masses
which fall upon the earth from space.

Extraction of Iron from its Ores. — The extraction of iron
from its ores is theoretically simple, the essential steps
being these:

(1) The conversion of the ore into the oxides, unless the
oxides themselves are used.

This is accomplished by roasting them. If sulphides are
roasted the sulphur passes off as sulphur dioxide, and the
iron remains as the oxide. In roasting, further, water is
driven off, and the carbonate is decomposed into the oxide
and carbon dioxide.

(2) Eeduction of the Oxides by means of charcoal or
coke.

This is accomplished by mixing the ore with the reduc-

200

THE ELEMENTS OF CHEMISTRY.

ing agent and heating in a blast-furnace. The blast-furnace

is constructed of fire-brick and
masonry. It is from 50 to 90 feet
high, and from 15 to 18 feet wide
in the widest part. An idea of
the construction is given by Fig.
39. Alternate layers of ore and
fuel are introduced into the top of
the furnace. A flux is also added.
This is usually limestone or quick-
lime. The object of the flux is to
form a fusible substance with the
earthy constituents of the ore. As
the iron is reduced it melts, and
the compound formed with the flux
also melts. The molten iron being
the heavier liquid, it sinks to the
bottom followed by the other,
which is called the slag. The iron
collects in the bottom of the furnace, called the crucible,
and is drawn off in the liquid condition.

Pig-iron. — The iron drawn off from the furnace is called
pig-iron. It is always impure, containing phosphorus,
sulphur, silicon, and as much as 2 to 6 per cent of carbon.
It is brittle and easily fusible, and is used for casting,
being known as cast-iron.

Wrought-iron. — When the carbon, silicon, and phos
phorus are removed from pig-iron it becomes very tougl
and malleable. It is now tvrought-iroji. Oast-iron is con-
verted into wrought-iron in one of two ways :

(1) By melting it and blowing air into the molten mass.

Fig. 39.

THE IRON FAMILY.

201

The carbon, phosphorus, and silicon are thus oxidized and
gotten rid of. This process is known as puddling.

(2) By mixing cast-iron with some of the purer ores and
heating to a high temperature, when the carbon, phos-
phorus, etc., are oxidized by the oxygen of the ores.
This process is called cementation.

Steel. — Steel is a third variety of iron which contains 1
to 2 per cent of carbon; more than wrought and less than
cast iron. It has the property of becoming extremely hard
and brittle when heated and suddenly cooled. When cau-
tiously heated and allowed to cool slowly it is rendered
elastic. This process is called tempering.

There are two ways of making ateel:

(1) Wrought-iron is heated with charcoal or with iron
containing carbon. This is known as the cementation pro-
cess, and is the opposite of the cementation process for
making wrought-iron.

(2) Cast-iron is melted in a large vessel called a con-
verter (see Fig. 40), and then partly
oxidized by currents of air forced into
the mass. Oast-iron is now added, and
steel containing any desired proportion
of carbon thus made. This is known as
the Bessemer process.

Pure Iron. — Pure iron is almost un-
known. It is a white metal with a
strong lustre. In moist air it rusts;
that is, it becomes covered with a layer
of oxide and hydroxide which is formed
by the action of the air and water. The Fig. 40.

wire used for pianos is nearly pure; but if this be dissolved
in hydrochloric or sulphuric acid, small black particles of

202 THE ELEMENTS OF CHEMISTRY.

carbon will remain undissolved. The odor noticed when
ordinary iron is dissolved in acid is due to the presence of
impurities.

Compounds of Iron. — Iron, like mercury and copper,
forms two series of compounds which differ markedly from
each other. These are the ferrous and ferric compounds.
Thus with chlorine it forms two chlorides, one of which,
ferrous chloride, has the composition expressed by the for-
mula FeCl2; the other, ferric chloride, by FeCl3. It appears
from a study of the relative weights of these chlorides in
the state of vapor (see Chapter XIV., page 126) that the
above formulas should be doubled, so that ferrous chloride
is now commonly represented by Fe2Cl4, and ferric chlo-
ride by Fe2Cl6. For our purpose the simpler formulas
will answer just as well. Similarly there are two oxides,
FeO and Fe203; two sulphates, ferrous sulphate, FeS04,
and ferric sulphate, Fe2(S04)3, etc.

Change of Ferrous to Ferric Compounds. — Ferrous com-
pounds pass into ferric compounds by simple contact with
the air; and are readily converted by oxidizing agents,
such as nitric acid, potassium chlorate, etc. When, for
example, ferrous hydroxide, Fe(OH)2, is exposed to the
air suspended in water, it changes to ferric hydroxide,
Fe(OH)3. The change is represented by the equation

2Fe(OH)2 + H20 + 0 = 2Fe(OH)3.

So, also, when ferrous chloride is left standing in hydro-
chloric acid solution it changes to ferric chloride, and the
change is rapidly effected by boiling with a little nitric
acid:

2FeCl8 + 2HC1 + 0 = 2FeCl3 + H30.

THE IRON FAMILY. 203

Ferrous Chloride, FeCla, is formed by dissolving iron in
hydrochloric acid.

Experiment 11 9. —Dissolve a little iron wire in dilute hydro-
chloric acid. Hydrogen is evolved, accompanied by small quan-
tities of other gases whose formation is due to the presence of
impurities in the iron, and carbon is left undissolved as a black
residue. To a few drops of the solution in water in a test-tube
add at once caustic soda. This precipitates ferrous hydroxide,
Fe(OH)2, which changes color rapidly, becoming finally reddish
brown. Pure ferrous hydroxide is white. As it passes to the
ferric condition it becomes dirty green, and darker and darker
until it is reddish brown, which is the color of ferric hydroxide,
Fe(OH)3. Heat another small portion of the solution of ferrous
chloride to boiling, add two or three drops of concentrated nitric
acid and boil again. Kepeat this operation two or three times.
The ferrous chloride is thus oxidized to ferric chloride. It will be
noticed that the color of the solution after the oxidation is red-
dish yellow, whereas before the oxidation it was nearly colorless
or slightly greenish. Add caustic soda to the solution of ferric
chloride. A reddish-brown precipitate of ferric hydroxide will be
formed. Just as in this case you have passed from ferrous
chloride to ferric chloride by oxidation, so you can pass back
again to the ferrous compouud. Thus, by adding a little zinc to
a solution of ferric chloride in which hydrochloric acid is present,
the hydrogen evolved extracts chlorine from the ferric chloride
and converts it into ferrous chloride:

FeCl3 + H = FeCl2 + HC1.

Ferrous Sulphate, FeS04 + 7HaO.— This salt, which is
commonly known as "green vitriol" or "copperas/' is
formed by the action of sulphuric acid on iron. [What is
" White vitriol "? " Blue vitriol " ?] It is extensively used
in the preparation of ink and in dyeing.

Inks. — Iron inks are made by treating solutions of tannic
acid, which is obtained from nut-galls, with ferrous sul-
phate or copperas. There are many kinds of ink in use

204 THE ELEMENTS OF CHEMISTRY.

which are not made in this way. Printers' ink contains
lamp-black. So also does India ink. Inferior inks are
made of aniline dyes, which are made from coal-tar.

Iron Alum, FeK(S04)2 + 12H20, is formed by bringing
ferric sulphate and potassium sulphate together. It re-
sembles ordinary alum, A1K(S04)2 + 12H20, but differs
from it in containing iron instead of aluminium.

Ferric Oxide, Fe203, occurs in nature in lustrous crystals,
as hematite, and as a red mass. It is prepared on the large
scale by heating copperas in the air, when the change rep-
resented in the following equation takes place:

2FeS04 = Fe203 + S03 + S02

The oxide thus obtained is a dark-red powder called
rouge. ■ It is used for polishing glass and as a paint.

Ferroso-ferric Oxide, Fe304, or magnetic oxide of iron,
is found in nature in the form of loadstone. It is formed
when iron is burned in oxygen (see Experiment 26).

The sulphides of iron have been repeatedly mentioned.

Ferrous Sulphide, FeS, is made by heating sulphur and
iron together in proper proportions. It is used in making
hydrogen sulphide. [Explain how.]

Iron Pyrites, FeS2, is a yellow crystallized substance
very abundantly found in nature. When heated in a
closed tube sulphur is given off. When heated in an open
vessel as upon a shallow iron pan or spoon, the sulphur is
oxidized to sulphur dioxide, and the iron is left in the
form of the oxide. [Verify these statements by experi-
ment.]

Nickel, M {At. Wl. 58.5), is found in meteoric iron and
in combination with arsenic. It forms two series of salts

THE IRON FAMILY. 205

corresponding to the two hydroxides nickelous hydroxide,
Ni(OH)2, and nickelic hydroxide, Ni(0H)3O Nickel is
used for making coins, and for plating other metals. It is
not acted upon by the air.

Cobalt, Co {At. Wt. 59.1), is found in combination with
arsenic and sulphur, and also in small quantities accom-
panying nickel in meteoric iron.

Cobalt compounds are used on account of their colors*
Smalt is made by fusing glass with a cobalt compound,
when a blue mass is obtained which is powdered and used
as a paint. When cobaltic oxide and aluminium oxide are
fused together a dark-blue substance is formed which is
known as cobalt ultramarine.

206 THE ELEMENTS OF CHEMISTRY.

CHAPTER XXIII.
MANGANESE— CHROMIUM— URANIUM-BISMUTH.

Manganese, Mn (At. Wt. 55).— Manganese is found in
nature in the form of the oxides., of which manganese di-
oxide, or the black oxide of manganese, occurs most abun*
dantiy. With oxygen it forms the following compounds:
manganous oxide, MnO; manganic oxide, Mn203; manga-
noso-manganic oxide, Mn304; manganese dioxide, Mn02;
and permanganic anhydride, Mn207.

Manganese presents points of resemblance with aluminium
and iron. Like iron it forms two series of salts, the man-
ganous and manganic series, which diJffer from each other
very much as ferrous and ferric compounds do.

Chromium, Or (At. Wt. 52.3). — This element is com-
paratively rare, and occurs almost only in combination
with oxygen and iron as chromic iron, Fe0r20^

Potassium Chromate, K2Cr04, is formed when finely-
powdered chromic iron is heated with potassium carbonate
and potassium nitrate.

Potassium Dichromate, K2Cr207. — This is the form in
which chromium is most frequently met with. It is formed
from the chromate by adding acetic or nitric acid. The
change which takes place is represented thus:

2KfOrO% + 2HN03 = 2KN03 + K2Cr207 + H20.

The relation between the chromate and the dichromate
will be more readily understood by considering the acids

MANGANESE— CHROMIUM— URANIUM— BISMUTH 207

from which they are derived. These are chromic acid,
H2Cr04, and dichromic acid, H2Cr207. The latter may be
regarded as derived from the former by loss of water:

2H2Cr04 = H2Cr207 + H20.

Experiment 120. — Potassium dichromate is converted into the
chromate by adding a solution of potassium hydroxide until the
color becomes pure yellow:

K2Cr207 + 2KOH = 2K2Cr04 + H20.

Convert 10 to 20 grams potassium dichromate into the chro-
mate. Evaporate to crystallization. Compare the salt thus
obtained with potassium dichromate0

Experiment 121. — Convert the potassium chromate just ob-
tained into potassium dichromate by adding dilute nitric acid
until the color is red. Evaporate to crystallization.

Both the chromate and dichromate are good oxidizing

agents,

Experiment 122. — Treat a little of each salt in a test-tube with
hydrochloric acid. [What evidence do you get that the salts are
good oxidizing agents ?]

Chrome-yellow. — The chromates of lead and barium are

insoluble in water. They are yellow. The lead salt is the

well-known paint chrome-yellow.

Experiment 123. — Add a little of a solution of potassium chro-
mate or dichromate to a solution of barium chloride, and of lead
acetate or nitrate.

Chrome Alum is a salt related to ordinary alum, but con-
taining chromium instead of aluminium. Its formula is
CrK(S04)2 + 12H20. The alums have analogous formulas;

Ordinary alum , . . . A1K(S04)2 + 12H20;

Iron alum. FeK(S04)2 + 12H20;

Chrome alum CrK(S04)2 + 12HaO.

208 THE ELEMENTS OF CHEMISTBY.

Uranium, U {At. Wt. 239). — This element occurs mostly
in the form of the oxide IT304 known as pitchblende.

Bismuth, Bi {At. Wt. 208), occurs mostly native, and is ob-
tained by heating the ores and allowing the molten bismuth
to run out. In appearance it closely resembles antimony.

Bismuth forms alloys which melt at low temperatures.
The best known of these is "fusible metal/' which is com-
posed of lead, tin, and bismuth.

The chief compound of bismuth and oxygen is the yellow
oxide Bi203, which is formed when bismuth is burned in
the aire

The principal salt of bismuth is the nitrate Bi(NOs)8 +
5HaO. It is used in medicine.

LEAD-TIN— PLATINUM-GOLD. 209

CHAPTER XXIV.
LEAD— TIN— PLATINUM— GOLD.

Lead, Pb {At. Wt. 207). — Lead occurs in combination in
several forms in nature, as, for example, in the sulphate,
carbonate, chromate, and sulphide. The sulphide, PbS,
known as galena, or galenite, is the most important ore of
lead.

Extraction of Lead from its Ore. — The extraction of lead
from its ore is accomplished in one of two ways:

(1) By heating the sulphide with iron, when the latter
combines with the sulphur, forming iron sulphide, while
the lead is set free.

(2) By roasting the sulphide until it is partly converted
into lead oxide and lead sulphate; then heating the mixture
without access of * air, when the two reactions take place
which are represented in these equations:

PbS + 2PbO =3Pb + SOf;
PbS + PbS04 = 2Pb + 2S02.

The lead is thus set free, and the sulphur driven off as
sulphur dioxide.

Properties of Lead. — Lead is a bluish-gray metal with a
high lustre. It is soft and not very strong. It melts at
about 325°. All lead salts are poisonous. Nitric acid dis-
solves it, but hydrochloric and dilute sulphuric acids do
14

210 THE ELEMENTS OF CHEMISTRY.

not. It is precipitated in metallic form from a solution of
one of its salts by metallic zinc. The formation is some-
times called the " lead-tree" or " Arbor Saturni."

Experiment 124.— Dissolve 30-40 grams lead acetate (sugar of
lead) in a litre of water, add a few drops of acetic acid, and put
the solution in a wide-mouthed bottle. Suspend a piece of sheet-
zinc in the middle of the solution, and let it stand. The lead will
be deposited slowly in crystallized form. At the same time the
zinc will pass into solution. The zinc simply takes the place of
the lead:

Zn + Pb(N03)2 = Zn(N03)2 + Pb.

fre-

Lead Water-pipes. — Pipes for conveying water are
quently made of lead, and under most circumstances there
is no danger in this; but some waters, particularly such as
are rich in carbon dioxide, act upon lead and dissolve it in
small quantity. Such waters are exceedingly dangerous.
If air and water together act upon lead, it is much more
readily acted upon than when the air is excluded. In
moist air lead tarnishes.

Experiment 125. — Cut a piece of sheet-lead an inch or two
square and partly cover it with water in a shallow dish. Allow
it to stand for several days, renewing the water from time to time.
Then filter off and examine the solution to see whether there is
any lead in solution. This is done by taking advantage of the
fact that lead chloride is difficultly soluble, and lead sulphate and
sulphide insoluble, in water. (1) To a little of the solution in a
test-tube add a few drops of hydrochloric acid. Is a precipitate
formed? (2) To another small portion of the solution add a few
drops of sulphuric acid. Is a precipitate formed? (3) Into a
third portion pass a little hydrogen sulphide. What change takes
place ? Try the same experiments with a very dilute solution of
lead acetate.

Oxides of Lead. — Lead forms three compounds with oxy-
gen, viz.: lead suboxide, Pb20; lead oxide, PbO; and load

LEAD— TIN— PLA TINUM—GOLD. 211

peroxide, Pb02. Red lead, or minium, is apparently a
mixture of the oxide and peroxide, and has approximately
the composition Pb304.

Lead Oxide, PbO, is commonly known by the name lith-
arge. It is formed by the oxidation of molten lead in con-
tact with the air. In the separation of lead from silver
advantage is taken of this fact. Silver does not combine
with oxygen when heated in the air. Therefore when a
mixture of lead and silver is heated in the air to the proper
temperature the lead is converted into the oxide, while the
silver remains unchanged. The lead oxide thus formed is
easily separated from the silver.

Minium, Red Lead, Pb304 (= 2PbO + PbO,).— When
litharge is heated in the air to 400° it takes up oxygen and
is converted into minium, or red lead. When minium is
heated to a high temperature it gives up oxygen and is
again converted into yellow lead oxide. Treated with ni-
tric acid, a part is dissolved, forming lead nitrate, while
lead peroxide, a brown powder, remains behind.

Experiment 126. — Treat a little minium with ordinary dilute
nitric acid, and note the change in color. Does lead pass into
solution ? How do you know ?

Lead Peroxide, Pb02, conducts itself somewhat like man-
ganese dioxide. When treated with hydrochloric acid
chlorine is evolved:

Pb02 + 4HC1 = PbCl, + 2H20 + 201.

Experiment 127.— Treat a little lead peroxide with hydrochloric
acid in a test-tube. In what form is the lead after the experiment ?
Is the product soluble or insoluble in water ?

The sulphate, chromate, and chloride have already been
referred to. They are formed by adding a soluble sulphate,

212 THE ELEMENTS OF CHEMISTRY.

chromate, and chloride to a solution of a lead salt. The
chromate is the well-known chrome-yellow.

Lead Carbonate, PbC03, is the well-known and much-
used pigment white lead. The objection to its use in a
laboratory is that it turns black in the presence of even
small quantities of hydrogen sulphide. Zinc-white does
not act in this way, as zinc sulphide is a white substance.

Tin, Sn (At. Wt. 118). — Tin occurs in nature mostly as
tin-stone? which is the oxide Sn02. The metal is obtained
from the ore by reducing with charcoal. It is a white metal
which resembles silver in appearance. It is soft and mal-
leable, and can be hammered out into very thin sheets,
forming the well-known tin-foil. At 200° it is brittle; and
at 228° it melts. It does not change in the air at ordinary
temperatures. Ordinary concentrated nitric acid oxidizes
it, the product being a compound of tin, oxygen, and hy-
drogen, known as metastannic acid, ^ which is a white pow-
der insoluble in nitric acid and in water.

Extraction of Tin from its Ore. — The oxide or tin-stone is
pulverized, mixed with charcoal, and heated in a furnace,
when the tin appears in the molten condition.

Uses of Tin. — Owing to the fact that tin does not change
in the air it is used as a covering for other metals. Ordi-
nary tin-ware is made of sheets of iron covered with tin.
An inferior variety of tin- ware is manufactured containing
lead. If such ware is used for cooking-utensils or for making
cans for preserving fruit and vegetables serious results may
follow, as the acids of the foods may dissolve enough lead to
form poisonous liquids. Copper covered with tin is also
used for various purposes, as for bath-tubs and pins.

Alloys of Tin. — Among the valuable alloys containing tin
are solder, which consists of tin and lead j britannia,

LEAD— TIN— PLATINUM— GOLD. 21 3

which consists of 9 parts of tin and 1 part of antimony;
bronze and bell-metal, which consist of tin and copper.

Soldering. — Soldering in general is any process by which
metals are made to adhere by means of other metals added
in the molten condition. Ordinary soldering consists in
joining metals together by means of a solder consisting of
about equal parts of lead and tin. In order that the solder
may hold it is necessary that the surfaces of the metal to
which it is applied should be bright. This is brought
about by the use of resin or by washing with a little acid and
then adding some borax, which in the molten condition dis-
solves any metallic oxides which may be present, leaving the
surfaces bright. There is some danger in the use of solder
for tin cans, as it is possible for the contents to get in con-
tact with the solder unless the work is done with unusual
care.

Stannous and Stannic Compounds. — Tin forms two classes
of compounds, the stannous and stannic compounds. These
do not bear to each other the same relation as that which
exists between cuprous and cupric compounds, or that be-
tween ferrous and ferric compounds. In stannous com-
pounds the tin appears to be bivalent, as indicated by
the formulas Sn012, SnO, SnS, which respectively repre-
sent stannous chloride, oxide, and sulphide. In stan-
nic compounds, on the other hand, the tin appears to be
quadrivalent, as indicated by the formulas SnCl4, Sn02,
SnS2, which respectively represent stannic chloride, oxide,
and sulphide.

Stannous Chloride, SnCl2, and Stannic Chloride, SnCl4,
are the most used compounds of tin. They find application
in dyeing. The former is known as tin-salt. It is made by
dissolving tin in hydrochloric acid.

214 THE ELEMENTS OF CHEMISTRY.

Stannic Sulphide, SnS2, is a yellow substance used under
the name mosaic gold as a pigment in decorating.

Platinum, Pt {At. Wt. 194.8.), occurs almost always
accompanied by the rare metals iridium, palladium, and os-
mium, in the form of alloys. The ore is found in the
Ural Mountains, in California, Australia, and a few other
places. It is prepared by treating the ore with strong
aqua regia, which dissolves the platinum, together with
some iridium. The platinum chloride thus obtained is
precipitated by means of ammonium chloride, with which,
as with potassium chloride, it forms a difficultly soluble
compound, (NH4)2PtCl6. When this is heated to a suffi-
ciently high temperature it is decomposed, leaving me-
tallic platinum behind.

Properties of Platinum. — Platinum is a grayish-white
metal with a high lustre. Its specific gravity is 2L15, it
being one of the heaviest substances known , The specific
gravity of iron is 7.8, that of lead 11.4. In other words, a
piece of platinum weighs nearly three times as much as a
piece of iron of the same dimensions, and nearly twice as
much as a piece of lead of the same dimensions. Platinum
is not dissolved by hydrochloric, nitric, or sulphuric acid ;
but aqua regia dissolves it, forming platinum chloride,
Pt014. Fusing caustic alkalis attack it ; sodium carbon-
ate does not. It does not change in the air, and does not
melt except in the flame of the oxyhydrogen blow-pipe.
It resists the action of most substances.

Uses of Platinum. — The properties of platinum make it
extremely valuable to the chemist. Platinum crucibles
and evaporating-dishes, foil, and wire are in constant use
in every laboratory, and it is difficult to see how we could
get along without them. Large retorts of platinum are

LEAD— TIN— PLA TINUM— G OLD. 216

used for the purpose of concentrating sulphuric acid and
distilling it.

Gold, Au (At. Wf. 196.7). — Gold usually occurs native.
It is found enclosed in quartz, or more frequently in quartz
sand. It is separated mechanically by washing, and then
extracted with mercury, which forms an amalgam with it.
The amalgam is afterwards heated, when the mercury
passes oyer and the gold remains behind.

Properties of Gold. — Gold is a yellow metal with a high
lustre. It is quite soft and extremely malleable. It can
be beaten into leaves not more than y^-J^ of a millimetre
thick. Its specific gravity is 19.3. It combines directly
with chlorine, but not with oxygen. Hydrochloric, nitric,
and sulphuric acids do not act upon it ; but aqua regia
dissolves it, forming gold chloride. On account of the
fact that gold resists the action of other substances it was
formerly spoken of as the Icing of metals, and therefore
the mixture of hydrochloric and nitric acids which dis-
solves it was called aqua regia, or royal water.

Uses of Gold. — Gold ware and coin are made of an alloy
of gold and copper. The standard gold coin of the United
States contains nine parts of gold to one of copper. The
composition of gold for jewelry is usually stated in carats.
Pure gold is 24-carat gold ; 20-carat gold contains 20 parts
gold and 4 parts copper ; 18-carat gold contains 18 parts
gold and 6 parts copper, etc.

236 THE ELEMENTS OF CHEMISTS F.

CHAPTEK XXV.
SOME FAMILIAR COMPOUNDS OF CARBON.

Organic Chemistry. — When the compounds which are
obtained from plants and animals were first studied it was
supposed that they were entirely different in every way
from the compounds obtained from earthy or mineral sub-
stances. The former were called organic substances, for
the reason that they were obtained from organized beings ;
while the latter were called inorganic substances. Organic
substances were the subject of Organic Chemistry, and inor-
ganic substances formed the subject of Inorganic Chemis-
try. These names are still in use, though they have lost
their original meaning. Organic Chemistry means now
only the Chemistry of the Compounds of Carbon.

Occurrence of the Compounds of Carbon. — The most widely
distributed compound of carbon is carbon dioxide, which,
as you have learned, is the starting-point of all life on the
globe. All living things are formed from it either directly
or indirectly. The substances which exist in the vegeta-
ble kingdom in largest quantity are cellulose and starch;
but besides these a very large number of other substances
are found, as the sugars, — the alkaloids of which, mor-
phine, quinine, and nicotine, are examples, — oxalic acid,
malic acid, tartaric acid, citric acid. In the animal king-
dom, too, occur many substances, as albumin, fibrin, etc.

Formation of the Compounds. — Certain natural processes

COMPOUNDS OF CARBON. 217

which are not throughly understood have giyen rise to the
formation of a complex mixture of organic compounds,
principally hydrocarbons, in petroleum (page 106).

Distillation of Coal. — The destructive distillation of coal
for the purpose of making illuminating-gas, and the forma-
tion 3f coal-tar, have already been referred to. Coal-tar is
one of the most important sources of compounds of car-
bon. The hydrocarbons benzene, C6H6, toluene, C7H8,
xylene, C8H10, naphthalene, C10H8, anthracene, C14H10,
etc., are obtained from this source.

Distillation of Wood. — Wood is heated in closed vessels
mostly for the purpose of making charcoal, as already ex-
plained. Among the products obtained from this source
are ivood-spirit, or methyl alcohol, and pyrolig neons acid,
or acetic acid. Large quantities of acetic acid are pre-
pared in this way.

Distillation of Bones. — In order to make bone-black,
bones are subjected to destructive distillation. The oil
which passes over is collected and known as bone-oil. Of
late this has proved to be the source of a large number of
compounds which are of special interest on account of
their connection with the valuable alkaloids, quinine, mor-
phine, etc.

Fermentation. — A number of the most important com-
pounds of carbon are formed by a process known as fer-
mentation. This is a general term meaning any process in
which a chemical change is effected by means of minute
animal or vegetable organisms. The best known example
of fermentation is that of sugar, which gives rise to the
formation of ordinary alcohol.

Classes of Compounds of Carbon. — The chief classes of
these compounds are the hydrocarbons, some of which have

218

THE ELEMENTS OF CHEMISTRY.

already been treated (see pages 107); the alcohols; the
acids; the ethers; and the ethereal salts. First a few of
the best known examples of each of these classes will be
taken up, and afterwards some other familiar compounds
which do not belong to any one of these classes.

Alcohols.

Methyl Alcohol, Wood-spirit, 0H40. — This is formed by
the distillation of wood, and is separated from the other
products which are formed at the same time. It has,
when pure, a pleasant odor and taste and acts upon the
animal system very much as ordinary alcohol does. It
burns without giving light or smoke, and may therefore be
used in lamps for heating purposes as ordinary alcohol is.
It is used in the manufacture of varnishes.

Ethyl Alcohol, Spirits of Wine, C2H60.— This well-
known substance is formed by the fermentation of grape-
sugar or glucose.

Experiment 128. — Dissolve 20 to 30 grams commercial grape-
sugar, or 20 to 30 cc. table sy-
rup, in 1 to 2 litres of water
in a flask. Connect the flask
by means of a bent glass tube
with a cylinder or bottle con-
taining clear lime-water. The
vessel containing the lime-water
must be provided with a cork
with two holes. Through one
of these passes the tube from
the fermentation-flask; through the other a tube connecting with
a vessel containing solid caustic potash, the object of which is to
prevent the air from acting upon the lime-water. The arrange-
ment of the apparatus is shown in Fig. 41. Now add to the so-
lution of grape-sugar or syrup a little fresh brewer's yeast; close
the connections and allow to stand. Soon an evolution of gas

Fig. 41.

COMPOUNDS OF CABBOJST. 219

will begin, and, as this passes through the lime-water, a precipi-
tate will be formed which can be shown to be calcium carbonate.

What Change takes place in the Sugar ? — If the solution
in the flask is examined carefully it will be found to contain
alcohol and no sugar. Grape-sugar has the composition
expressed by the formula C6H1206. By fermentation it is
decomposed, forming alcohol, C2H60, and carbon dioxide,
C02. The decomposition is expressed by the equation

C6H1206 = 2C2H60 + 2C02

What Causes the Change ? — It has been found that the
change of grape-sugar is caused by small organized bodies
which grow in the solution. These bodies are contained
in ordinary yeast.

Germs in the Air. — When fruit-juices which contain
sugar are exposed to the air they undergo fermentation
without the addition of yeast. This is due to the fact that
the germs or seeds of the bodies which cause fermentation
are everywhere 'floating in the air. Hence, when a liquid
in which these seeds can grow is exposed to the air, the
bodies are formed, and fermentation takes place.

Different Kinds of Fermentation. — The fermentation
which yields alcohol is only one of many kinds. Among
the others are: (1) lactic-acid fermentation, which takes
place in the souring of milk; and (2) acetic-acid fermenta-
tion, which causes the transformation of alcohol into acetic
acid. The latter ferment is contained in " mother of
vinegar."

Distillation of Fermented Liquids. — In order to get the
alcohol from liquids which have undergone fermentation
they must be distilled. For this purpose very perfect

'220 THE ELEMENTS OF CHEMISTRY.

forms of stills have been devised, so that the alcohol passes
over nearly free from other substances. Usually it con-
tains impurities known ^ fusel oil.

Properties of Alchol. — Pure ethyl alcohol has a peculiar,
pleasant odor. It remains liquid at very low temperatures,
but has recently been converted into a solid at a tempera-
ture of — 130.5°. It burns with a flame which does not
deposit soot, and was hence formerly much used in labora-
tories for heating purposes, and is still used where gas can-
not be obtained. Its effects upon the human system are
well known. It intoxicates when taken in dilute form,
while in large doses it is poisonous. It lowers the temper-
ature of the body when taken internally, although it
causes a sensation of warmth.

Uses of Alcohol. — Alcohol is the principal solvent for or-
ganic substances. It is hence extensively used in the arts,
as in the manufacture of varnishes, perfumes, and tinctures
of drugs. The many beverages in use owe their intoxicat-
ing power to the presence of alcohol. The milder forms
of beer contain from 2 to 3 per cent;, light wines about 8
per cent; while whiskey, brandy, etc., sometimes contain
as much as 60 to 75 per cent.

Glycerin, C3H803. — Glycerin is an alcohol which occurs
very widely distributed as a constituent of fats. The rela-
tion it bears to the fats will be explained when the acids
which enter into the fats are taken up. It is obtained from
the fats by boiling them with an alkali like caustic soda or
caustic potash, or by heating with steam.

Properties. — Glycerin is a thick, colorless liquid with a
sweetish taste. It attracts moisture from the air, and is
hence used to keep surfaces moist.

COMPOUNDS OF CARBON- 221

Acids.

Formic Acid, CH202. — This acid occurs in nature in red
ants, in stinging-nettles, in the shoots of some of the vari-
eties of pine, and elsewhere. It is a colorless liquid.
Dropped on the skin, it causes extreme pain and produces
blisters.

Acetic Acid, C2H402. — This is the acid contained in vine-
gar which gives to it its value. It is formed from alcoholic
liquids by exposing them to the air, in consequence of the
presence of a microscopic organism which is contained in
what is commonly known as "mother of vinegar." The
formation of acetic acid from alcohol is due to the action
of oxygen as represented in the equation

C2H60 + 0, = 02H402 + H.O.

Alcohol. Acetic acid.

But oxygen alone does not effect the change. When the
ferment is present the oxidation takes place. Acetic acid
is also obtained by distilling wood. Hence the names
pyroligneous acid and wood-vinegar.

Properties. — Acetic acid is a clear, colorless liquid. It
has a very penetrating, pleasant, acid odor, and a sharp
taste. The pure substance acts upon the skin like formic
acid, causing pain and raising blisters.

Uses.- — Acetic acid is extensively used, chiefly in the
dilute form known as vinegar. It is used in calico-print-
ing in the form of iron and aluminium salts. With iron it
gives hydrogen, which is needed in the manufacture of cer-
tain compounds used in making dyes.

Salts of Acetic Acid. — The best-known salts of acetic acid

222 THE ELEMENTS OF CHEMISTRY.

are lead acetate, Pb (02H302)2, commonly called sugar of
lead; and copper acetate, Ou (02H302)2, a variety of which
is known as verdigris.

Fatty Acids. — Formic and acetic acids are the first mem-
bers of an homologous series (see page 108). Some of the
more important members are named in the following table:

Formic acid CH202.

Acetic " C2ELO2.

Propionic " CsH602.

Butyric " dHsO.,.

Palmitic " Ci6H3202.

Stearic " Ci8H8602.

They are called fatty acids for the reason that many of
them are obtained from fats.

Butyric Acid, C4H802, is of special interest because it is
obtained from butter by boiling with caustic potash. It
occurs also in many other fats. There is a lutyric-acid
ferment contained in putrid cheese which has the power of
converting sugar into butyric acid.

Palmitic Acid, 016H3202, is obtained from many fats., but
palm-oil is especially rich in it.

Stearic Acid, C18H3602, is the acid contained in the fat
known as stearin. The so-called "stearin candles" are
made of a mixture of palmitic and stearic acids.

Soaps. — Soaps are the alkali salts of the acids contained

in fats, especially of palmitic and stearic acids. Fats are

compounds of these acids with glycerin. When the fats

are boiled with an alkali, as caustic soda, the corresponding

salts of the acids are formed, while the glycerin is set free.

The palmitate and stearate of potassium and sodium are

the soaps.

Experiment 129. — In an iron pot boil a quarter of a pound of
lard with a solution of 40 grams caustic soda in 250 cc. of water

COMPOUNDS of carbon: 223

for an hour or two. After cooling add a strong solution of
sodium chloride. The soap formed will separate and rise to the
top of the solution, where it will finally solidify. Dissolve some
of the soap thus obtained in water.

Use of Soap. — The cleansing power of soap depends upon
the fact that it dissolves the oily film on the surface of the
skin and thus facilitates the removal of the foreign sub- ,
stances commonly known as dirt.

Action of Soap on Hard Waters. — As has been explained,
a hard water is one which contains salts in solution.
Temporary hardness is that which is caused by calcium
carbonate held in solution in the water by carbon dioxide.
Permanent hardness is caused by calcium sulphate or mag-
nesium salts. The calcium and magnesium salts of pal-
mitic and stearic acids are insoluble in water. Therefore,
when soap is added to a hard water these insoluble salk
are precipitated, and give the water a hard feeling. In
attempting to wash the hands with soap in a hard water
they become covered with a thin layer of the insoluble salts
which prevents them from rubbing freely over each other,
and makes them feel sticky. Before the soap can do any
good all the lime-salt must be precipitated. The action in
the case of temporary hardness is represented by the equa-
tion

2Na016H31Oa + CaC03 = Ca(C16H3I02), + Na,C03.

Soap. Calcium palmitate.

In the case of permanent hardness it is represented by
the equation

2NaCl6H3102 + CaS04 = Ca(C16H3102), + Na,S04.

Experiment 130. — Make some hard water by passing carbon
dioxide through dilute lime-water until the precipitate first formed

224 THE ELEMENTS OF CHEMISTRY.

is dissolved again. Filter. Make a solution of soap by shaking
up a few shavings of soap with water. Filter. Add the solution
of soap to the hard water. Is a precipitate formed ? Rub a piece
of soap between the hands wet with the hard water.

Experiment 131. — Make some hard water by shaking a litre or
two of water with a little powdered gypsum. Perform with it the
same experiments as those first performed with the water contain-
ing calcium carbonate.

Relations of the Soap Industry to other Industries. — A

great chemist and philosopher has said that the quantity of
soap used in a country is a measure of the civilization of
the country. Certain it is that soap is only used by
civilized people, and that by them it is used in enormous
quantities. In many farm-houses a primitive method for
the manufacture of soap is practised, consisting in treating
refuse fats with the lye extracted from wood-ashes. A soft
soapy mass is thus obtained known as " soft-soap." Fats
form the starting-point in the manufacture of all soap.
These are generally treated with caustic soda. Caustic
soda is all made from sodium carbonate by the action of
lime ; and, as you have learned, sodium carbonate is made
from common salt mostly by the Leblanc process, which
requires sulphuric acid. Thus the manufacture of sul-
phuric acid and sodium carbonate is intimately related to
the manufacture of soap.

Oxalic Acid, C2H204. — This acid occurs very widely dis-
tributed in nature, as in the sorrels, which owe their acid
taste to the presence of acid potassium oxalate, KC2H04;
and as the ammonium salt in guano. It is probably one of
the first substances formed from carbon dioxide in the plant.
It is manufactured by heating wood shavings or sawdust
with caustic soda and caustic potash. Oxalic acid is an

COMPOUNDS OF CARBOK 225

active poison. It is used in calico-printing, and in clean-
ing brass and copper surfaces.

Lactio Acid, C3H603. — Lactic acid is made by the fer-
mentation of sugar by means of the lactic-acid ferment.
The reaction effected by the ferment is represented by the
equation

C6H1206 = 2C3H60,

Malic Acid, C4H605. — This acid is very widely distributed
in the vegetable kingdom, as in apples, cherries, etc.

Tartaric Acid, C4H606. — Tartaric acid occurs very widely
distributed in fruits, sometimes uncombined, sometimes in
the form of the potassium or calcium salt; as, for example,
in grapes, berries of the mountain-ash, potatoes, cucum-
bers, etc., etc. It is prepared from " cream of tartar."
This is acid potassium tartrate, which is formed when
grape-juice ferments.

Citric Acid, C6H807. — Citric acid, like malic and tartaric
acids, is very widely distributed in nature in many varieties
of fruit, especially in lemons. It is also found in currants,
whortleberries, raspberries, gooseberries, etc., etc. It is
prepared from lemon-juice: 100 parts of lemons yield 5^
parts of the acid. It is a solid, crystallized substance, sol-
uble in water. It is frequently used for the purpose of
making lemonade without lemons, and there is no objection
to its use for this purpose.

Ethees.

Ether, C4H:oO. — Ordinary ether is the best-known repre-
sentative of the class of compounds called ethers. It is

formed from ordinary alcohol by treating it with sulphuric
15

226 THE ELEMENTS OF CHEMISTRY.

acid and distilling. The result of the action which takes
place is represented by the equation

2C,H60 = C4H100 + H20.

Alcohol. Ether.

Ether is a liquid which boils at a low temperature and
takes fire and burns readily. Inhaled it produces insensi-
bility to pain. It is therefore called an ancesthctic.

Ethereal Salts.
Action of Acids upon Alcohols. — When an acid acts upon
an alcohol it is neutralized, though not as readily as when
it acts upon a base. The product is a substance which re-
sembles a salt and is called an ethereal salt. Thus when
nitric acid acts upon alcohol this reaction takes place:

02H60 + HN03 = O.H.NO, + H20.

The product C2H5lSr08, called ethyl nitrate, is an ethereal
salt. The alcohol acts as if it were a substance like caus-
tic potash and made up thus, C2H5 .OH. The resemblance
between its action and that of caustic potash is shown by
the equations

KOH + HN03 = KNO3 + H20, and
C2H6OH + HNO3 = O.H.NO, + H20.

Saponification. — When an ethereal salt is boiled with a
caustic alkali it is decomposed, the products being an alco-
hol and an alkali salt. Thus when ethyl nitrate is boiled
with caustic potash, potassium nitrate and alcohol are
formed:

CaH,NOs -f KOH = C2H6OH f KNO,

COMPOUNDS OF CARBON-. 227

This process is called saponification, because the most
important example is furnished by soap-making.

Fats. — The fats are ethereal salts in the formation of which
glycerin, as the alcohol, and three acids take part. The
three acids are palmitic and stearic acids, already mentioned,
and oleic acid, C18H3402. Although the composition of
these substances is comparatively complex, the way they act
upon one another is simple, and is the same as the action
of nitric acid upon alcohol in forming ethyl nitrate. The
fats, then, are the palmitate, stearate, and oleate of glyceryl,
which bears to glycerin very much the same relation that
ethyl, C2H5, bears to alcohol. When a fat is boiled wit-i
caustic soda, then, the sodium salts of the acids, contained
in the fat, and glycerin are formed.

Butter consists of ethereal salts of glycerin and sev-
eral fatty acids, among which are palmitic, stearic, and bu-
tyric acids. Oleo-margarin is an artificial butter made
from other fats than that from milk.

Ethereal Salts as Essences. — The ethereal salts generally
have pleasant odors, and it is to their presence that many
fruits owe their flavors. Some of the compounds are now
made artificially and used instead of the natural extract of
the fruit. Thus the ethyl salt of lutyric acid is used
under the name of essence of pineapples, and the amyl salt
of valeric acid under the name essence of apples.

Nitroglycerin.— Among the more important ethereal
salts of glycerin are the nitrates. Two of these are known,

(O.N02

viz., the mono-nitrate, C3H5 \ OH , and the tri-nitrate,

(OH

C3H5(0 . N02)3, the latter being the chief constituent of

nitroglycerin. Nitroglycerin is prepared by treating gly-

228 THE ELEMENTS OF CHEMISTRY.

cerin with a mixture of concentrated sulphuric and nitric
acids. It is a pale yellow oil which is insoluble in water.
At — 20° it crystallizes in needles. It explodes very vio-
lently by concussion. It may be burned in an open vessel,
but if heated above 250° it explodes. Dynamite is infu-
sorial earth* impregnated with nitroglycerin. Nitrogly-
cerin is the active constituent of a number of explosives.

Eelatioks between the Compounds Considered.

Comparison of the Formulas. — On comparing the formu-
las of the hydrocarbons of the marsh-gas series (see page
107) with those of the simplest alcohols and the fatty
acids, it will be seen that these compounds are all related
in a simple way. Below are lists of a few of the hydro-
carbons, alcohols, and acids:

Hydrocarbons.

Alcohols.

Acids.

CH4

CH40

ch2o2

C2H6

02H60

C2H402

C3H8

C3H80

c3h6o2

C4H10, etc.

C4H10O,

etc.

C4He02, etc

Each of these series is an homologous series.

Alcohols. — Alcohols have been shown to be derived from
the hydrocarbons by the replacement of one or more hydro-
gen atoms by oxygen and hydrogen, OH, or from water
by replacing one of the hydrogen atoms of the water by a
compound of carbon and hydrogen. An alcohol, then, is
a hydroxide, just as a metallic base is; only, instead of con-

*That is to say, earth made up of the microscopic flinty shells
which constitute the fossil remains of certain minute and simple
plants.

COMPOUNDS OF CABBON. 229

sisting of a metal in combination with hydrogen and
oxygen, it consists of a compound of carbon and hydrogen
in combination with hydrogen and oxygen. Thus:

Metallic Bases. Alcohols.

K(OH) CH3(OH)

Na(OH) C2H5(OH)

More Complex Alcohols. — Just as lime is a more complex
base than caustic potash, as shown by the formulas KOH
and Ca02H2 or Ca(OH)2, so there are more complex alco-
hols than ordinary alcohol. A good example is furnished
by glycerin, C3H803, which has been shown to be a hydrox-
ide corresponding to aluminium hydroxide, Al(OH)3, a
fact which is represented by the formula C3H.(OH)3. It
may be called glyceryl hydroxide, the complex, C3HB, be-
ing known as glyceryl.

Radicals or Residues. — The compounds of hydrogen and
carbon contained in the alcohols are called radicals or resi-
dues. So we may say that an alcohol is water in which
half of the hydrogen has been displaced by a radical.

HOH 02H5OH

Water. Ordinary alcohol.

HOH ( OH

HOH 03H5 \ OH = C3H803.

HOH ( OH

Water. Glycerin.

Acids. — Just as the alcohols have been shown to be de-
rived from water, so the organic acids have been shown to
be derived from carbonic acid. Carbonic acid itself is not
known. But the carbonates are derived from an acid of

the formula H8C03, or CO -J qtt. If, in this acid, a hy-

230 THE ELEMENTS OF CHEMISTRY.

droxyl be replaced by a radical, as, for example, by ethyl,

(OH
02H&, a substance of the formula CO -J qW 5 or C3H602 is

the result. If methyl, CH3, be introduced in place of

ethyl, the product is CO -J qjt3 or C2H402, which is acetic

acid. In a similar way all the organic acids are derived
from carbonic acid.

COMPOUNDS OF CARBON. 231

CHAPTEK XXVI.
OTHER COMPOUNDS OF CARBON.

The Carbohydrates. — The carbohydrates form an im-
portant group of carbon compounds which include the
most abundant substances found in the vegetable kingdom.
They contain, besides carbon, hydrogen and oxygen in the
proportions to form water. Hence they are called carbo-
hydrates. The chief compounds included under this head
are grape-sugar or glucose, cane-sugar, starch, cellulose,
gum, and dextrin.

Grape-sugar, Glucose, Dextrose, 0BH1206. — Dextrose oc-
curs very widely distributed in the vegetable kingdom,
particularly in sweet fruits. It is found also in honey and,
further, in the liver and the blood.

Formation of Dextrose. — Dextrose or glucose is formed
from several of the carbohydrates by boiling with dilute
mineral acids, or by the action of ferments. Its forma-
tion from cane-sugar takes place according to this equa-
tion, equal quantities of dextrose and levulose being
formed:

0„H„011 + H20 = C.H.,0. + C6HI206.

Cane-sugar. Dextrose. Levulose.

Its formation from starch is represented by this equa-
tion:

06H10O6 + H2O = C6H12O,

Starch. Dextrose.

232 THE ELEMENTS OF CHEMISTRY.

Manufacture of Dextrose or Glucose. — Dextrose is pre
pared on the large scale from corn-starch in the United
States, and from potato-starch in Germany. The change
is usually effected by boiling with dilute sulphuric acid,
The acid is afterwards removed by treating with chalk, and
filtering. [Explain how this removes the acid.] The
filtered solutions are evaporated either to a syrupy consis-
tency, and sent into the market under the names " glu
cose," " mixing-syrup/' etc., or to dryness, the solid pro-
duct being known as " grape-sugar. "

Properties. — Dextrose crystallizes from concentrated so-
lutions, and as seen in commercial "granulated grape-
sugar " looks very much like granulated cane-sugar. It
is sweet, but not as sweet as cane-sugar. It is estimated
that the sweetness of dextrose is to that of cane-sugar as
3 : 5. Under the influence of yeast it ferments }Tielding
mainly alcohol and carbon dioxide. Putrid cheese trans-
forms it into lactic acid, and then into butyric acid.

Levulose (Fruit-sugar), C6H1206. — This form of sugar
occurs with dextrose in fruits; and is formed by the action
of dilute acids or ferments on cane-sugar, which breaks up
according to the equation

0MH„On + H20 = C6H1206 + C6H1206.

Cane-sugar. Dextrose. Levulose.

As cane-sugar is found in unripe fruits, it is probable
that the change represented in the equation takes place
during the process of ripening.

Cane-sugar, C12H22On. — This well-known variety of sugar
occurs very widely distributed in nature — in sugar-cane,
sorghum, the Java palm, the sugar-maple, beets, madder-

COMPOUNDS OF CABBON. 233

root, coffee, walnuts, hazel-nuts, sweet and bitter almonds;
in the blossoms of many plants, etc., etc.

Sugar-refining. — Sugar is obtained mainly from the
sugar-cane and beets. In either case the processes of ex-
traction and refining are largely mechanical. When sugar-
cane is used, this is macerated with water to dissolve the
sugar. Thus a dark-colored solution is obtained. This is
evaporated, and then passed through filters of bone-black
by which the color is removed. The clear solution is then
evaporated in open vessels to some extent; and, finally, in
large closed vessels called " vacuur:i-pans," from which the
air is partly exhausted, so that the boiling takes place at a
lower .temperature than would bo required under the ordi-
nary pressure of the atmosphere. The mixture of crystals
and mother-liquors obtained from the "vacuum-pans" is
freed from the liquid by being brought into the "centrifu-
gals." These are funnel-shaped sieves which are revolved
rapidly, the liquid being thus thrown by centrifugal force
through the openings of the sieve, while the crystals re-
main behind and are thus nearly dried. The final drying
is effected by placing the crystals in a warm room.

Molasses. — The mother-liquors obtained from the " cen-
trifugals" are further evaporated, and yield lower grabes of
sugar; and, finally, a syrup is obtained which does not
crystallize. This is molasses.

Properties of Sugar. — Sugar crystallizes from water in
large well-formed prisms. When heated to 210° to 220°,
cane-sugar loses water, and is converted into a substance
called caramel, which is more or less brown in color. When
boiled with dilute acids, cane-sugar is split into equal parts
of dextrose and levulose. The mixture of the two is called
invert-sugar. Yeast gradually transforms cane-sugar into

234 THE ELEMENTS OF CHEMISTBY.

dextrose and levulose, and these then undergo fermenta-
tion. Cane-sugar does not ferment.

Sugar of Milk, Lactose, CiaHaaOn + H20.— This sugar
occurs in the milk of all mammals. It is obtained in the
manufacture of cheese. Cows' milk consists of water, ca-
sein, butter, sugar of milk, and a little inorganic material,
in about the following proportions:

Water.. 87 percent.

Casein 4 "

Butter 3£ "

Sugar of milk 4f "

Mineral matter f "

100

Cheese is made by adding rennet to the milk, which
causes the separation of the casein. The sugar of milk re-
mains in solution, is separated by evaporation, and puri-
fied by recrystallization. It has a slightly sweet taste, and
is much less soluble in water than cane-sugar.

Souring of Milk. — Sugar of milk ferments under certain
circumstances, and is transformed mostly into lactic acid.
The souring of milk is a result of this fermentation. The
lactic acid formed coagulates the casein j hence the thick-
ening.

Cellulose, 06H10O5. Cellulose forms, as it were, the
groundwork of all vegetable tissues. It presents different
appearances and different properties, according to the
source from which it is obtained ; but these differences are
due to substances with which the cellulose is mixed ; and
when they are removed, the cellulose left behind is the
same thing, no matter what its source may have been
The coarse wood of trees and the tender shoots of the

-•'"-*-•■■— "-•'-'- -

:

COMPOUNDS OF CARBON. 235

ton-wool, hemp, and flax consist almost wholly of cellu-
lose.

Properties. — Cellulose does not crystallize, and is insol-
uble in all ordinary solvents. It dissolves in concentrated
sulphuric acid. If the solution be diluted and boiled, the
cellulose is converted into dextrin and dextrose. It will
thus be seen that rags, paper, and wood, all of which con-
sist largely of cellulose, might be used for the preparation
of dextrosa or glucose, and consequently of alcohol.

Gun-cotton, Pyroxylin, Nitro-celluose. — Cellulose has
some of tie properties of alcohols; among them the power
to form ethereal salts with acids. Thus, when treated with
nitric acid it forms several nitrates, just as glycerin forms
the nitrates known as nitro-glycerin (which see). The
nitrates are explosive, and are used for blasting under the
name gun-cotton.

Collodion. — A solution of gun-cotton in a mixture of
ether and alcohol is known as collodion solution, which is
much used in photography. When poured upon any sur-
face, such as glass, the ether and alcohol rapidly evaporate,
leaving a thin coating of the nitrates.

Celluloid. — Celluloid is an intimate mixture of gun-cot-
ton and camphor. As it is plastic at a slightly elevated
temperature, it can easily be moulded into any desired
shape. When cooled it hardens.

Paper. — Paper in its many forms consists mainly of cel-
lulose. The essential features in the manufacture of paper
are, first, the disintegration of the substances used. This
is effected partly mechanically and partly by boiling with
caustic soda. Then the resulting mass is converted into
ptilp by means of knives placed on rollers. The pulp,
with the necessary quantity of water, is then passed be-

236 THE ELEMENTS OF 0HEMI8TBZ

tween rollers. Chiefly rags of cotton or linen are used in
the manufacture of paper; wood ^nd straw are also used.

Starch, C6H10O5. — Starch is found everywhere in the
vegetable kingdom in large quantity, particularly in all
kinds of grain, as maize, wheat, etc. ; in tubers, as the po-
tato, arrowroot, etc.; in fruits, as chestnuts, acorns, etc.

Manufacture of Starch. — In the United States starch is
manufactured mainly from maize; in Europe, from pota-
toes. The processes made use of are mostly mechanical.
The maize is first treated with warm water; the softened
grain is then ground between stones, a stream of water
running constantly into the mill. The thin paste which
is carried away is brought upon sieves of silk bolting-cloth,
which are kept in constant motion. The starch passes
through with the water as a milky fluid. This is allowed
to settle when the water is drawn off. The starch is next
treated with water containing a little alkali, the object of
which is to dissolve gluten, oil, etc. The mixture is now
brought into shallow, long wooden runs, where the starch
is deposited, the alkaline water running off. Finally, the
starch is washed with water, and dried at a low tempera-
ture.

Properties. — Starch in its usual condition is insoluble in
water. If ground with cold water it is partly dissolved.
If heated with water the membranes of the cells of which
the starch is composed are broken, and the contents form a
partial solution. On cooling, it forms a transparent jelly
called starch-paste. By dilute acids and ferments starch
is converted into dextrin, maltose, and dextrose.

Flour. — Wheat flour, which may serve as an example of
flour in general, contains water, starch with a little sugar
and gum, gluten, and a small quantity of mineral matter.

COMPOUNDS OF CARBON. 237

The finest flour contains about 10 per cent of gluten and
70 per cent of starch. Gluten is a substance which re-
sembles in many respects the white of eggs, or egg-albu-
min.

Bread-making. — The chemical changes which take place
in bread-making are of special interest. Bread is made by
mixing the flour with water and a little yeast. The dough
thus prepared is put in a warm place for a time, when it
rises. The rising is a result of fermentation caused by the
yeast. A part of the starch contained in the flour is con-
verted into sugar, and this is then converted into alcohol
and carbon dioxide by fermentation. The alcohol passes
off for the most part, and the carbon dioxide in striving to
escape from the thick gummy dough fills the mass with
bubbles of gas, making the mass light and porous. When
the loaf is put into the oven the gases contained in it ex-
pand, making it still lighter; then the fermentation ]s
checked and no further chemical change takes place except
on the surface, where the substances are partly decomposed
and converted into a dark-colored product, the crust,

A Few Compounds from Coal-tab.

Aromatic Compounds. — The fact that benzene, CfcH6,
toluene, C7Hg, and other hydrocarbons are obtained from
coal-tar has already been mentioned (p. 217). These hy-
drocarbons are the starting-points for the preparation of a
very large number of compounds of carbon which are com-
monly called the "aromatic compounds/'' as many of them
have a pleasant aromatic odor.

Nitrobenzene, C6H6N02. — This substance is formed by
treating benzene with nitric acid:

238 THE ELEMENTS OF CHEMISTRY.

C6H6 + HN08 = C.H.NO + H,0.

It is a yellow liquid which has a pleasant odor like that of
the oil of bitter almonds. It is much used under the name
artificial oil of bitter almonds.

Aniline, C^H.NH,. — When nitrobenzene is treated with
any solution from which hydrogen is given off the oxygen
is extracted and replaced by hydrogen :

C8H6N02 + 6H = CeH6NH2 + 2H50.

The product is the substance known as aniline. It is a
colorless liquid. When treated with mercuric chloride
(corrosive sublimate, HgCl2) or arsenic acid it is con-
verted into the dye magenta, which is the substance from
which the aniline dyes are prepared.

Aniline Dyes. — Of these a large number are in use.
They are all derivatives of rosaniline, of which magenta is
a salt. A great many different colors of aniline dyes are
made, some of them of great beauty.

Phenol, Carbolic Acid, C6H60. — This familiar substance
is contained in coal-tar, and is extracted from it by treat-
ing with caustic soda in which the carbolic acid dissolves.
When pure it crystallizes in beautiful colorless rhombic
needles. It has a peculiar, penetrating odor, and is poi-
sonous. It is much used as a disinfectant.

Oil of Bitter Almonds,

, C„HttO. — This substance occurs
Benzoic Aldehyde,

in combination with amygdalin, which is found in bitter

almonds, laurel-leaves, cherry-kernels, etc. Amygdalin

belongs to the class of compounds known as glucosides,

which break up into glucose and other substances. Amyg-

COMPOUNDS OF CARBON 239

dalin itself, under the influence of emulsin, which oc-
curs with it in the plants, breaks up into oil of bitter al-
monds, hydrocyanic acid, and dextrose :

C20H2,NOU + 2H20 = C,H60 + CNH + 2C6HI20f.

Amygdalin. Oil of Hydrocy- Glucose,

bitter anic acid,

almonds.

It is prepared from bitter almonds, which yield about 1.5
to 2 per cent, It is a liquid which has a pleasant odor.
It is made artificially from coal-tar, and is used in the
preparation of artificial indigo.

Benzoic Acid, C7H602. — Benzoic acid occurs in gum ben-
zoin and in the balsams of Peru and Tolu, and is made ar-
tificially from coal-tar by oxidizing toluene,* C7H8.

Balsams and Odoriferous Resins. — The balsams of Peru
and Tolu are thick fragrant fluids which are obtained from
certain trees in South America and elsewhere by cutting the
bark. Benzoin is a similar substance. These as well as
myrrh, frankincense, and other substances of the kind are
used for their odors. The odors are increased when the
substances are heated. Hence they are largely used as in-
cense.

Gallic Acid, 07H605. — Gallic acid occurs in sumach, in
Chinese tea, and many other plants. It is formed by boil-
ing tannin or tannic acid with sulphuric acid. It is pre-
pared from gall-nuts by fermentation of the tannin con-
tained in them. It is closely related to tannin or tannic
acid.

Tannic Acid, Tannin, 014H 0O9. — This substance occurs

* The name toluene conies from the fact that this hydrocarbon was
first obtained from the balsam of Tolu.

240 TEE ELEMENTS OE CHEMISTRY.

in gall-nuts, from which it is extracted in large quantities.
It is soluble in water. Its solution gives a dark blue-black
color with iron salts. Tannin is used extensively in medi-
cine, in dyeing, in the manufacture of leather and of ink.

Experiment 132. — Boil 10 grams of powdered gall-nuts with
60 cc. of water, adding water from time to time. A solution of
tannin is thus obtained. Filter after standing. In a test-tube
add to some of this solution a few drops of a solution of copperas
(ferrous sulphate). A colored precipitate is formed which gradu-
ally changes to black.

Tanning. — The process of tanning consists in treating
hides from which the hair has been removed with an in-
fusion of hemlock or oak bark, or of sumach leaves, in
which there is tannic acid. The acid combines with certain
parts of the hides, forming insoluble compounds which
remain in the pores, converting the hides into leather.

Indigo. — In several plants which grow in the East and
West Indies, in South America, Egypt, and other warm
countries, there occurs a substance called indican which,
when treated with dilute mineral acids and certain fer-
ments, breaks up into indigo-blue and a substance resem-
bling glucose. Commercial indigo contains as its princi-
pal ingredient indigo-blue. Indigo-blue is now prepared
artificially by first making the oil of bitter almonds from
coal-tar and further transforming this by complicated pro-
cesses.

Naphthalene, C10H8. — This is a hydrocarbon which is
contained in coal-tar in large quantity. It is a beautiful
white crystallized substance much used in the preparation
of dyes.

Anthracene, 0]4H10. — Anthracene like naphthalene is ob-
tained from coal-tar. Its chief use is in the preparation
of artificial alizarin.

COMPOUNDS OF CABBON. 241

Alizarin, C14H804. — Alizarin is the well-known dye
which is obtained from madder-root. For some years it
has been made artificially from anthracene, and the culti-
vation of madder has been largely given up. Madder-root
was used for dyeing "Turkey red." Artificial alizarin is
almost exclusively "used for this purpose at present.

Glucosides. — Glucosides are substances which occur in
nature in the vegetable kingdom, and which break up un-
der the influence of ferments and dilute acids into sugar
and other compounds. Amygdalin has already been men-
tioned. This breaks up into oil of bitter almonds and
dextrose. Indican, which yields indigo and dextrose, is
another example.

Myronic Acid, another glucoside, is found in the form of
the potassium salt in black mustard-seed. When treated
with myrosin, which is contained in the aqueous extract of
white mustard-seed, potassium myronate is converted into
dextrose and oil of mustard.

Alkaloids.— These are compounds occurring in plants,
frequently being those parts of the plants which are most
active when taken into the animal body. They are hence
sometimes called the active principles of plants. Many of
these substances are used in medicine. They all contain
nitrogen and in some respects resemble ammonia. Only a
few of the more important alkaloids need be mentioned
here.

Quinine. — This valuable alkaloid is obtained from the
outer bark of certain trees which grow in Peru. The
bark is known as Peruvian bark. There is some hope that
quinine will be prepared artificially before long.

242 THE ELEMENTS OF CHEMI8TBT.

Cocaine is found in cocoa-leaves. Its hyc ,chloric-acid
salt has recently come into prominence in medicine, owing
to the fact that a small quantity of its S0x .xon placed
upon the eye or the gums or injected beneath the skin
causes insensibility to pain.

Nicotine occurs in tobacco-leaves in combination with
malic acid.

Morphine and Narcotine are the principal alkaloids found
in opium, which is the evaporated sap that flows from in-
cisions in the capsules of the white poppy before they are
ripe.

QUESTIONS AND PROBLEMS.

CHAPTER I.

What two kinds of changes are you familiar with?

Give some familiar illustrations of each.

What is the chief difference between the two kinds of change?

Mention some examples of physical changes which are not given in
the book.

Mention some examples of chemical changes not given in the book.
Why do you call these changes chemical changes?

What is meant by saying that physical and chemical changes are
related?

Give some familiar examples which make these relations clear.

How does the steam-engine illustrate these relations?

Suppose a stone should fall upon some gunpowder and cause it to
explode, which would be physical and which chemical change?

Give some examples showing that heat can cause chemical changes.

Give some examples showing that chemical changes can produce
heat.

Give examples showing that in some cases when substances are
simply brought together chemical changes are caused.

Give some examples showing that solution aids chemical action.

How can we distinguish chemical action from all other kinds of
action?

What is the difference between a mixture and a chemical compound?

How can this difference be illustrated by means of iron and sul-
phur?

Suppose sugar and sand were placed together in a vessel and well
shaken up, would a chemical compound or a mechanical mixture be
formed? Try the experiment, and see whether you can answer the
question with the aid of the experiment. Treat the substance with
water ; what takes place? What is left?

When iron and sulphur combine chemically, is there any gain or
loss in weight?

Explain the difference between elements and compounds.

Is wood an element? Why?

Is the number of compounds larger than the number of elements?

How many elements enter into the composition of the things with
which we generally have to deal?

244 THE ELEMENTS OF CHEMISTRY.

Give some examples of elements. Why are they called elements?

Give some examples of compounds. Why are they called com-
pounds?

In general, what is meant by chemical action?

What three kinds of chemical action are there? Give examples of
each.

Why does a stone fall to the earth when thrown upward?

Why do substances act chemically upon one another?

Suppose chemical attraction should cease, what would be the result?

Which of the elements is most abundant? Which comes next in
order?

Which is the principal element that enters into the composition
-of living things?

How are the Dames of the elements formed? Give examples.

What is meant by the symbols of the elements?

CHAPTER II.

Describe the changes which are produced in lead, zinc, and tin by
heating them, and describe the experiments which taught you what
these changes are.

How did you learn that the air had anything to do with these
changes?

Did heat have anything to do with the changes? Suppose you
knew that the bits of metal used in Experiments 13, 14, and 15 in-
creased in weight when heated in the air, and that they did not in-
crease in weight when heated so that the air could not get at them,
what would that show ?

What familiar facts show that the air has something to do with
burning?

How could you find out what the air does when things burn in it?

What is noticed when a candle is burned in a closed vessel ?

Does a candle in burning gain or lose in weight?

How much of the air is used up when anything burns in a closed
vessel?

Suppose a substance is burned in a closed vessel containing air and
gains 5 grams in weight, where would this 5 grams of matter come
from? How much would you expect to fiiiiL that the air had lost in
weight?

What is the composition of the air?

Why are oxygen and nitrogen called elements?

CHAPTER III.

Where and in what quantity is oxygen found?

How can we get oxygen from the air?

Explain how oxygen is collected when it is set free from the oxide
of mercury.

What other ways are there of getting oxygen ?

What is the appearance of oxygen? Its smell? taste? What hap
pens to it when it is much cooled down and compressed?

QUESTIONS AND PBOBLEMS. 245

How does oxygen behave towards other substances at the ordinary
temperature? How do you know this? Does oxygen act upon any-
thing at the ordinary temperature? Give examples.

Of what importance is oxygen to all animals? What difference is
there between the action of oxygen at the ordinary temperature and
at higher temperatures? How did }rou learn this difference?

When substances burn in oxygen, is the oxygen used up? What
becomes of it? Do the substances gain or lose in weight? How
does the weight of the oxygen used up compare with the gain in
weight of the substance burned ?

What does burning in oxygen consist in?

Is burning in the air the same chemical act as burning in oxygen?
How can this be proved? Why do substances not burn as actively
in the air as they do in oxygen?

What is meant by combustion?

What are combustible substances?

What are incombustible substances?

Is water combustible? Is wood combustible?

Give an example of a substance which will not burn in the air, but
which will burn in oxygen. How was this shown?

What is meant by the kindling temperature? Explain why it is
that a stick of wood burns gradually and not all at once.

Explain the connection between the heat and light produced, and
the combustion of a substance.

What is meant by the expressions chemical work and chemical
energy ?

Do combustible substances possess chemical energy?

Show how a combustible substance can do work. What are the
substances called which are found in combustion? Give examples.

CHAPTER IV.

Explain what is meant by saving that the elements combine in
definite weights.

What is the law of definite proportions?

How are natural laws discovered?

What is a natural law?

In studying the proportions by weight in which the elements com-
bine with one another, what is observed?

What are the combining weights of the elements?

How is a chemical compound expressed by a symbol?

What does the symbol NaCl mean? What does O stand for?
What does Fe stand for?

How does a chemist express what takes place when mercury oxide is
heated?

How much mercury is contained in 20 grams of mercury oxide?

How much oxygen is contained in 30 grams of mercury oxide?

How much mercury oxide would be necessary to furnish 10 grams
of oxygen?

How much mercury oxide would be necessary to furnish 10 grams
of mercury?

246 THE ELEMENTS OF CHEMISTRY. -

Explain what is meant by the law of multiple proportions. Give
examples illustrating the law.
What do the symbols S02, C02, and H2S04 mean?

CHAPTER Y.

Where and in what forms is nitrogen found in nature?

How can we get nitrogen from the air?

Why do we use phosphorus for the purpose?

Describe the method of preparing nitrogen.

How can nitrogen be obtained from the air by the use of copper ?

What is the color of nitrogen? its taste? its odor? How does it
differ from oxygen in its conduct towards burning things? Could
animals live in it? Why? Suppose there were no nitrogen in the
air, how would our fires differ from the fires in the air?

What is the difference between a chemical compound and a mechan-
ical mixture?

Are nitrogen and oxygen chemically combined or mixed together in
the air?

What reasons can you give for your statement?

CHAPTER VI.

How can it be shown that water is contained in wood? in meat?

Is water present in large or small proportion in animal and
vegetable substances?

What is meant by water of crystallization?

What are efflorescent substances?

What are deliquescent substances?

Is water an element or a compound? How do you know?

Describe the experiment in which an electric current is passed
through water. What does the experiment show?

CHAPTER VII.

Where and in what forms is hydrogen met with in nature?

How is hydrogen obtained?

What takes place when a piece of sodium is thrown upon water?

What takes place when steam is passed over heated iron?

What is water gas, and how is it obtained?

Which are the common acids? What do they all contain? What
takes place when they are treated with metallic elements?

What is the most convenient method for preparing hydrogen?

Describe the process fully, and show how you can collect the hy-
drogen.

What are the properties of hydrogen?

How is it shown that hydrogen is lighter than air?

What relation is there between the weights of equal volumes of
hydrogen and oxygen?

If the weight of a certain bulk of hydrogen is 1 ounce, what would
be the weight of the same bulk of oxygen ?

QUESTIONS AND PBOBLEMS. 247

What relation is there between the combining weights of hydrogen
and oxygen and the weights of equal bulks of the two gases?

When we say that the combining weight of hydrogen is 1 and that
of oxygen 16, what is meant? What is meant when we say the com-
bining weight of iron is 56?

If we should call the combining weight of oxygen 100, what would
be the combining weight of hydrogen ?

What change takes place in hydrogen when it is cooled down very
much and greatly compressed ?

Does hydrogen combine with cxygen at the ordinary temperature?
How do you know ?

What takes place when it is heated in oxygen?

Does hydrogen support combustion? How can this be shown?

CHAPTER VIII.

Is water formed when hydrogen burns? How can this be shown?
How is it explained ?

What takes place when a flame or spark is applied to a mixture of
hydrogen and oxygen? How is this explained?

How can we show what takes place when a mixture of hydrogen
and oxygen explodes? What has been shown to take place? How
does this help us to understand what the composition of water is?

In what other way can the composition of water be found out?

Explain exactly how the experiment with copper oxide teaches us
whit the composition of water is.

What is meant by reduction? a reducing agent?

Explain the oxyhydrogen blow -pipe and its uses.

Explain the lime-light or Drummond light.

Has water any color?

Is the water which is found in nature pure? Why is this?

Why does ice float on water ?

What is the purest water found in nature? Why?

What is the character of the water found in mountain streams
which flow over sand-stone ? Why ?

What is the character of the water which flows over lime-stone?

What are mineral springs ?

How does water become salt?

What are effervescent waters ? chalybeate waters ? What is sul
phur water ?

What are the most common causes of impurities in water?

What change takes place in river-water which has been contam-
inated with drainage?

What precautions should be taken in regard to the position of
wells? Why?

How can water be purified ? Describe the process of distillation.

What kinds of substances cannot be removed from water by distil-
lation ?

What is meant by saying that water is the best solvent?

Why do we use solutions in studying the chemical action of sub-
stances upon one another?

248 THE ELEMENTS OF CHEMISTRY.

What is a solution?

What is expressed by the symbol H20?

In what respects do hydrogen and oxygen resemble each other? Id
what respects do they differ from each other?

Do hydrogen and oxygen combine readily? Does combination
take place more readily between those elements which are alike or be-
tween those which are unlike?

What change takes place in oxygen when electric sparks are passed
through it? In what other ways can this change be brought about?

How can ozone be converted into oxygen?

When oxygen is changed to ozone, and c zone to oxygen, is there
any change in weight?

What is hydrogen dioxide? How is it made? What is its most
striking property? What is it used for?

CHAPTER IX.

What is destructive distillation?

From what kinds of substances is ammonia given off in destructive
distillation?

What is one of the products formed when substances containing
carbon, hydrogen, and oxygen arc heated? In what experiment
which you have already performed is this shown?

Explain why ammonia is formed in gas-works?

What does the process of decay consist in?

What becomes of the nitrogen contained in animal substances when
they decay?

What connection is there between saltpetre and nitric acid? be-
tween potassium nitrite and nitrous acid ?

What is the "ammoniacal liquor" of the- gas-works? What is
formed when hydrochloric acid is added to this liquor:

How is ammonia obtained from ammonium chloride?

Express what takes place in a chemical equation, and explain exactly
what the equation means.

[The expression 2NH4C1 represents twice the quantity of ammonium
chloride that is represented by NH4C1. So also 2NH3 represents a
quantity of ammonia twice as great as is represented by NH3,]

How much ammonia can be obtained from 50 grams of ammonium
chloride?

The combining weight of nitrogen is 14, that of calcium, Ca, is 40,
and that of chlorine, CI, is 35.5. We have, therefore, these relations ;

2NH4C1 + CaO = 2NH3 + CaCl2 + H2C
2(14 + 4 + 35.5) + (40 + 16) = 2(14 + 3) + (40 + 71) + (2 + 16)

2X53.5 + 56 = 2x17 + 111 + 18

107~~ + 56 = 34 + 111 + 18

To determine the quantity of ammonia which can be obtained from
50 grams of ammonium chloride, we have simply to solve the propor-
tion

107 : 34 :: 50 : the weight of ammonia.

QUESTION'S AND PROBLEMS. 249

For from 107 parts by weight of ammonium chloride there are
formed 34 parts by weight of ammonia, and, therefore, as these fig-
ures are to each other so is 50, the actual weight of ammonium chlo-
ride used, to the weight of ammonia obtained.

Describe the process of preparing ammonia from ammonium
chloride. How is the gas collected? What is the appearance of
ammonia? What is its odor? What effect does it produce upon
breathing ? What about its weight ? How is this shown ? Explain
the use of ammonia for the purpose of making ice. Does ammonia
burn ? How does water act upon it ?

What is "spirits of hartshorn " ?

How is nitric acid formed in nature ?

How is nitric acid obtained from saltpetre ? Express in an equation
what takes place. Describe the apparatus used, and give the reasons
for the arrangement of the apparatus.

What is the appearance of pure nitric acid? What takes place
when it is boiled ? when the sun shines directly upon it ? How does
strong nitric acid act?

Tyhat is ordinary commercial nitric acid ? Why do substances burn
in strong nitric acid. Describe some experiments which illustrate
the power of nitric acid: What does the nitric acid give up to the
substances upon which it acts ?

What does nitric acid give up when a metallic element acts upon it?
Describe what further takes place, and why.

What is aqua regia, and why has it received this name?

What compounds does nitrogen form with oxygen ? How does this
series illustrate the law of multiple proportions ? What is the law of
multiple proportions ?

How isnitrous oxide formed ? How is it usually prepared ? Give
the equation representing the action, and state what it means.

What are the properties of nitrous oxide ?

How is nitric oxide made ? What takes place when it is brought in
contact with the air ? Why is the gas red which first appears in the
flask used in making nitric oxide ? and why does it afterwards become
colorless ? Give the equations which represent what takes place when
nitric acid acts upon copper, and explain what they mean.

How is nitrogen peroxide formed ? What are its chief properties ?
For what is it used ?

CHAPTER X.

What is meant by saying that oxygen belongs to a family of ele-
ments?

In what form does chlorine occur in nature ? in what quantity ?
What are all the chlorine compounds with which we have to deal
made from ?

What two steps are necessary in order to get chlorine out of sodium
chloride or common salt ? What resemblance is there between the
process for making hydrochloric acid from common salt and that of
making nitric acid from sodium nitrate ? What is formed besides
hydrochloric acid and nitric acid in each case ?

250 THE ELEMENTS OF CHEMISTRY.

How is chlorine made in the laboratory? "Why is this method not
well adapted to the commercial manufacture of chlorine?

Describe Deacon's process for the manufacture of chlorine.

Describe Weldon's process for the manufacture of chlorine.

Describe accurately the method of making chlorine used in the
laboratory. How is the chlorine collected? What takes place when
powdered antimony is introduced into chlorine? copper foil? flowers
and calico?

What is the appearance of chlorine? its odor? its action upon the
throat and nose? Is it heavier or lighter than air? What is its
action upon water? What is bleaching?

What is disinfection? What is " bleaching-powder" ? What other
name has it? Why is it valuable as a disinfecting agent?

Compare the action of hydrogen on oxygen and on chlorine.
What are the products? What are chlorides?

What is the simplest way of forming hydrochloric acid? What
difference is there between the action of a mixture of chlorine and
hydrogen and a mixture of hydrogen and oxygen? What art is de-
pendent upon chemical changes caused by light? Describe the
method of preparing hydrochloric acid. Give the equation express-
ing the action, and state what it means.

If 40 grams of common salt are used, how much hydrochloric acid
and how much sodium sulphate will be obtained?

How is the hydrochloric acid collected ? What are the properties
of hydrochloric acid? Give a connected account of all that you
learned about it in Experiment 65. How can the composition of hy-
drochloric acid be determined? What is the composition? What
happens to hydrochloric acid when it is treated with a metallic ele-
ment like zinc? when treated with an oxide like zinc oxide? When
treated with substances which give up oxygen readily?

How are the chief compounds of chlorine, hydrogen, and oxygen
obtained? What is potassium chloride? potassium hypochlorite?
potassium chlorate? What takes place when these compounds are
treated with sulphuric acid ? Express the reactions in equations, and
show how the reactions resemble one another. Compare the reactions
with that which takes place when sulphuric acid acts upon sodium or
potassium nitrate.

To which of the substances above mentioned is "bleaching-pow-
der" allied?

In what way does the series of compounds of chlorine with hydro-
gen and oxygen illustrate the law of multiple proportions? /

CHAPTER XI.

What takes place when an acid and a base are brought together ?

What are alkalies ? Mention some common acids ; some common
bases. How can you conveniently tell whether a substance is an acid
or a base ?

What did you learn in Experiment 66 ?

How can you determine what is formed when an acid acts upon a
base ? What is formed when hydrochloric acid acts upon caustic soda?

QUESTIONS AND PBOBLEMS. 251

nitric acid upon caustic soda? sulphuric acid upon caustic soda? hy-
drochloric acid upon caustic potash? nitric acid upon caustic potash?
sulphuric acid upon caustic potash?

What do the experiments performed in regard to the action of acids
upon bases teach ?

What is formed when a metallic element acts upon an acid ?

What is an acid? a base? a salt?

What is a metal?

Explain the use of the syllables ic and ous in naming acids ; of
hypo and per. Give the names and symbols of the compounds of
chlorine, hydrogen, and oxygen.

How are bases named?

Explain how salts are named. What is the name and formula of
the potassium salt of hypochlorous acid? of perchloric acid? of chloric
acid? of nitric acid?

What are the salts of hydrochloric acid called? Why?

What connection is there between acid properties and oxygen?

CHAPTER XII.

What takes place when animal and vegetable substances are heated
to a high temperature? Why is this? What takes place when they
are heated in the air?

Give a familiar example of the process of destructive distillation.
For what purpose is coal distilled ? wood ?

What are the principal forms in which carbon occurs in nature?
Mention some of the most common compounds of carbon.

What two forms of pure carbon are there?

Where are diamonds found, and what is the general appearance of
a diamond when first found?

How can graphite be made? Compare graphite and diamond, stat
ing the properties of each. By what other names is graphite known?

What is amorphous carbon?

Describe the process by which charcoal is made.

Compare the properties of charcoal with those of diamond and
graphite.

What is coke, and how is it obtained? lampblack? bone-black or
animal charcoal?

What are charcoal filters used for? What are bone-black filters
used for?

What is the object of charring piles which are exposed to the action
of air and water?

What different kinds of coal do we distinguish between? What is
lignite? peat?

How was coal formed ?

What are the chief products of the destructive distillation of coal?
Are hard or soft coals used in the manufacture of illuminating-gas?
Why?

How can it be proved that diamond, graphite, and charcoal consist
only of the element carbon? What common properties have the dif-
ferent forms of carbon?

252 THE ELEMENTS OF CHEMISTRY.

What is meant by the name allotropism?

How can we form an idea in regard to the reason why one and the
same thing can appear in different forms?

Compare the chemical conduct of carbon with that of the other
elements thus far considered.

What is formed when carbon combines directly with oxygen? How
can this be proved? How can we easily recognize carbon dioxide?

Explain what takes place when a mixture of charcoal and copper
oxide is heated ; when a mixture of arsenic and charcoal is heated.
Is there any resemblance between the action of hydrogen and of
charcoal on heated copper oxide?

Why is carbon called a reducing agent?

What important use is made of charcoal as a reducing agent?

CHAPTER XIII.

What are hydrocarbons? Are these easily formed in the labora-
tory? Under what circumstances are they easily and abundantly
formed?

What is petroleum? Why must it be refined before it is fit for use
in lamps? How is it refined? What is the product called?

What are some of the light products obtained when petroleum is
refined? What is paraffin ?

Give the names and symbols of the four simplest hydrocarbons
coutained in petroleum.

What is meant by homology, and an homologous series?

Give the names and symbols of the first three members of the ethy
lene series.

Give the names and symbols of the first two members of the acety-
lene series.

Give the names of the first three members of the benzene series.

Where is marsh-gas found, and under what circumstances is it
formed? What are the final products of the oxidation of vegetable
matter? What is the chief product of the reduction of vegetable
matter?

Of what importance is the occurrence of marsh-gas in coal-mines?

How is marsh-gas made in the laboratory?

What are the properties of marsh-gas?

How is ethylene obtained, and what are its properties? What other
name has it?

How is acetylene formed, and what are its properties?

Describe in brief the method of making coal-gas.

What is coal-tar? Mention some of the products obtained from it.

What is the principal compound of carbon and oxygen?

Where and. in what forms is carbon dioxide found?

What processes which are constantly taking place give rise tc the
formation of carbon dioxide ?

How is carbon dioxide most easily made ? Describe the process
accurately. Express the action by means of a chemical equation, and
state what it means.

What are the properties of carbon dioxide?

QUESTIONS AND PROBLEMS. 253

Why does not carbon dioxide burn ?

What is meant by the statement, " Carbon can do chemical work" ?
What resemblance is there between a piece of carbon and an ele-
vated body of water ?

What is soda-water, and how is it made ?

What connection is there between the breathing process and carbon
dioxide ? Is carbon dioxide poisonous ?

Why is the air in badly ventilated rooms bad to breathe V

Why is carbon dioxide apt to be found in old wells ? How can it
be detected if present in large quantity ?

What is choke-damp, and what does the name come from ?

Of what importance to plants is the carbon dioxide in the air ? Of
what importance is it to animals ? What resemblance is there between
the food of animals and the fuel burned in stoves ?

How does the carbon of animals and plants get back into the air
again ?

In what way is all life directly dependent upon the sun ?

How are carbonates formed ? What is the composition of sodium
carbonate ? of potassium carbonate ? What, then, is the composition
of carbonic acid ? What takes place when carbonic acid is set free
from carbonates ?

What takes place when carbon dioxide acts upon potassium hy-
droxide ? upon calcium hydroxide ? Give the equations representing
the action, and name the products.

What takes place when carbon dioxide is passed into lime-water
until no further action is observed ? What change occurs when the
solution thus obtained is boiled ?

What are hard waters ? How are they formed ? Why do we make
the distinction between temporary and permanent hardness ? What
objection is there to hard waters ?

How is carbon monoxide formed ? Explain its formation in open
grate fires. What is the blue flame at the top of a coal fire due to ?

Why is the use of water-gas sometimes objected to ?

How is carbon monoxide made ?

What are its properties ?

What danger is there connected with the use of coal stoves ? Why
is smouldering charcoal a dangerous thing to have in a room ?

Why is carbon monoxide a good reducing agent ?

Of what importance is it in the reduction of iron from its ores ?

What is a flame ? What is the difference between a candle and a
lamp ?

How can it be shown that when a burning gas is cooled down it is
extinguished ?

Explain the construction of the miner's safety-lamp, and the reason
for its use.

Why do some flames give light and others not ?

How are cyanides formed ? What is yellow prussiate of potash,
and how is it made ? What is potassium cyanide ? How is cyanogen
made ? What are its properties ?

Where is prussic acid found ? How is it made ? What are its
properties ?

254 THE ELEMENTS OF CHEMISTRY.

CHAPTER XIV.

What are the two principal laws governing chemical action ?

Do we know why substances combine according to the laws of defi
nite and multiple proportions ?

What is an hypothesis ? a theory ?

What theory has been suggested to explain the laws of definite and
multiple proportions ?

Show how this theory accounts for the facts ?

What is meant by the atomic weights ?

What is meant by the expression molecule ?

What are the symbols of the elements intended to represent ? the
symbols of compounds ?

Explain in full what the symbols HN03, H2S04, 1STH3, CH4, and
CO 2 are intended to represent. What relation is there between the
weight of a molecule and the weights of the atoms of which it is made
up ?

What is Avogadro's law.

How does Avogadro's law help us to determine the relative weights
of the molecules of gaseous substances ?

How are the atomic weights determined from the molecular
weights ?

What difference is there between chlorine, oxygen, nitrogen, and
carbon as shown by the symbols of their compounds with hydrogen ?
What is meant by the valence of an element ?

What is meant by a univalent element ? a bivalent element ? a
trivalent element ? a quadrivalent element ? Barium forms the com-
pound BaCl2 ; what is the valence of barium ? Sodium forms the
compound NaCI ; what is the valence of sodium ?

In the formation of potassium nitrate from nitric acid, how is the
valence of potassium shown ? When a bivalent element like calcium
forms a salt with nitric acid, how does the displacement of hydrogen
take place ? Calcium is bivalent. What is the symbol of its salt
with sulphric acid ? Explain this. What is the symbol of the sodium
salt of sulphuric acid ? What does this show with regard to the
valence of sodium ?

If magnesium, Mg, is bivalent, what is the symbol of its sulphate ?
of its nitrate ? of its chloride ? What is the basis for the distinction
between acid-forming and base-forming elements ? Give examples of
the two classes. What are these classes sometimes called ?

What is meant when we speak of a family of elements ?

What are the families of acid-forming elements ?

CHAPTER XV.

Name the members of the chlorine family.

Why is fluorine included in this family ?

In what forms does bromine occur in nature ?

How is bromine obtained from sodium bromide ? Give the equa-
tions representing the steps which must be taken, and explain what is
meant by them.

QUESTIONS AND PBOBLEMS. 255

What are the properties of bromine ? What are the chief d fferences
between bromine and chlorine ?

What is hydrobromic acid, and how is it formed ? What difference
is there in the conduct of common salt and of sodium bromide to-
wards sulphuric acid ? How is this explained ?

What compounds does bromine form with hydrogen and oxygen ?

In what forms does iodine occur in nature ? How is it obtained in
Scotland and France ? What is kelp ?

How is iodine obtained from sodium iodide ? Give the equations
representing the action, and explain what they mean.

What are the properties of iodine ? Compare chlorine, bromine,
and iodine, stating the points of resemblance and difference.

How can you easily tell whether a substance is an iodide or not ?

How is hydriodic acid obtained? How does it differ from hydro-
chloric and hydrobromic acids? What takes place when potassium
iodide is treated with sulphuric acid?

In what forms does fluorine principally occur in nature?

How is hydrofluoric acid made, and what are its properties? Give
the equation representing the action of sulphuric acid on fluor-spar?
What use is made of hydrofluoric acid? Can the substance be kept
in glass bottles?

What analogy is there between chlorine, bromine, and iodine, as far
as the compounds which they form are concerned ?

What relation is there between the atomic weights of chlorine, bro-
mine, and iodine?

CHAPTER XVI.

Name the members of the sulphur family. Why has sulphur been
known for a long time? Where is it found in nature? What is the
chief source of the sulphur of commerce? Name some of the princi-
pal compounds in which sulphur occurs in nature?

Describe the process by which sulphur is extracted from its ores.

How is crude brimstone refined ? What is the difference between
"flowers of sulphur" and "stick sulphur"? Give the properties of
sulphur. What changes does it undergo when it is distilled?

What two forms can sulphur be obtained in? How can it be thus
obtained? How do the two forms differ from each other?

How does sulphur act when heated in the air?

What are sulphides? How are they formed?

Can sulphur and hydrogen be made to combine directly? What
is formed? Where is' this compound found in nature? Under what
conditions is it formed?

How is hydrogen sulphide made in the laboratory? Explain what
takes place when sulphuric acid is used ; when hydrochloric acid is
used. How is the substance collected? What are its properties?
How does it behave towards water? towards metals? What takes
place when it is passed over heated iron? Is there any resemblance
between this action and that which takes place wiien steam is passed
over heated iron? Express both acts by chemical equations.

What takes place when hydrogen sulphide is passed through solu-
tions containing metals in the form of soluble salts?

256 THE ELEMENTS OF C&EMlSTBT.

How can hydrogen sulphide be used for the purpose of learning
what things are made of? What is formed when sulphur is burned
in the air? What is formed when sulphur dioxide takes up more
oxygen? What is the product of the action of sulphur trioxide on
water? What relation is there between sulphurous acid and sulphuric
acid?

Where is sulphur dioxide found in nature? How is it made in the
laboratory? Explain the reactions, giving the equations.

What are the properties of sulphur dioxide? What uses are made
of sulphur dioxide?

How are sulphites made? What is the composition of sodium sul-
phite? What takes place when sodium sulphite is treated with sul-
phuric acid? with hydrochloric acid? Compare these reactions with
those which take place when sodium carbonate, Na2C03, is treated
with sulphuric acid and with hydrochloric acid.

Mention some salts of sulphuric acid which are found in nature.
How is sulphuric acid made? Explain the action of nitric oxide in
oxidizing sulphurous acid.

Describe the manufacture of sulphuric acid. Describe the arrange-
ment of a leaden chamber.

What is oil of vitriol, and how is it obtained? How does sulphuric
acid act upon sodium chloride? upon potassium nitrate?

How does sulphuric acid act towards water? How does it act upon
organic substances which contain hydrogen and oxygen? What
change does it produce in wood? Explain the change.

Of what importance is sulphuric acid in the arts?

What marked difference in conduct is there between sulphuric acid
and hydrochloric and nitric acids?

What is a monobasic acid? a dibasic acid?

Define acid, normal, and neutral salts.

What is carbon disulphide? How is it made, and what are its prop-
erties?

Why are selenium and tellurium included in the sulphur family?

What relation is there between the atomic weights of sulphur, sele-
nium, and tellurium ? Has any similar relation been noticed in the
case of other elements?

CHAPTER XVII.

How does phosphorus occur in nature? What is a phosphate?

How is phosphorus made?

What are the properties of phosphorus?

Explain what takes place when phosphorus and iodine are brought
in contact with each other.

What is red phosphorus? How is it made from ordinary phos-
phorus? Compare the two varieties of phosphorus. How is ordinary
phosphorus made from red phosphorus?

Describe the changes which take place when phosphorus is burned
in the air or in oxygen, and the product dissolved in water.

How is ordinary phosphoric acid made? What salts does it form

QtmsTiows Ajsrn problems. 257

with sodium? What is normal calcium phosphate? Why is phos-
phoric acid called a tribasic acid?

In what compounds is the element arsenic found in nature? What
are its properties?

What compound does arsenic form with hydrogen ? What com-
pound of nitrogen is it analogous to? How is it formed? Explain
all that takes place in Experiment 98.

What are the properties of arsine? What is Marsh's test, and for
what is it used?

What is the substance which is usually called arsenic? How is it
obtained from the element arsenic, and from the compounds of ar-
senic with metals? What are its properties?

Explain what takes place when arsenic trioxide and charcoal are
mixed together and the mixture heated. In what form does antimony
chiefly occur in nature? What are its general properties?

Compare stibine and arsine.

In what forms does boron occur in nature? How is it prepared?
What are its properties?

What is borax, and from what acid is it derived?

Mention some of the principal compounds of silicon which occur in
nature. Is it a rare or common element? What other element does
it resemble in some respects?

Does silicon occur in nature in the uncombined state? How is the
element obiained?

Mention some of the varieties of silicic acid, aiid point out the rela-
tion which exists between them.

Mention some of the principal varieties of silicon dioxide which oc-
cur in nature.

What important manufactured product contains silicon?

CHAPTER XVIII.

What is meant by the name base-forming elements ? What name
is given to the elements which are not base-forming elements ? How
does the number of base-forming elements compare with the number
of acid-forming elements ?

What is meant by metallic properties ?

What are the chief classes of metal derivatives ?

What are minerals ?

What is meant by the term metallurgy ?

CHAPTER XIX.

What are the alkalies, and why are they so called ?

In what form is potassium found in nature ? Of what importance
is the element potassium to plants ? Where does the potassium
which the plants use come from ? What is left when wood is burned ?
Suppose you wanted potassium sulphate, and had only wood ashes
and sulphuric acid, how could you get it ?

In what other forms besides those mentioned does potassium occur
in nature \

17

258 THE ELEMENTS OF CHEMISTRY.

How is potassium obtained from its compounds ? What are its
properties ? Explain what takes place when potassium acts upon
water.

How is potassium iodide made ? Explain the reactions. What
takes place when potassium iodide is treated with sulphuric acid ?
What is potassium iodide used for ?

How is potassium hydroxide formed? What is its common name?
Explain the reaction which is used in making potassium hydroxide.
What are the properties of the hydroxide ? What change does it
undergo when exposed to the air ? Where is saltpetre found, and
under what conditions is it formed ?

Describe the saltpetre plantations. How is saltpetre used in mak-
ing sulphuric acid ? How is it used in making nitric acid ?

Give an account of the manufacture of gunpowder, and explain its
use as an explosive.

In what forms is sodium found in nature ? What are its proper-
ties ? How does it differ from potassium ?

What is meant by saying that sodium is a good reducing agent ?
What is sodium amalgam, and for what is it used ?

Where and in what quantities is sodium chloride found ?

How is salt obtained from natural sources ?

What are the properties of sodium chloride ?

What are the chief uses of salt ?

What is caustic soda, and how is it obtained ?

Where is sodium nitrate found ? Why can it not be used in mak-
ing gunpowder ? How can potassium nitrate be made from it ?

What is the common name of sodium sulphate ? In what impor-
tant manufacturing process is it obtained ? What percentage of
water of crystallization does it contain ? What change takes place in
it when it is left in contact with the air ? Is it deliquescent or efflor-
escent ?

Of what importance is sodium carbonate ? From what source was
it formerly obtained ?

How did Leblanc come to devise a method for making sodium car-
bonate ?

Describe Leblanc's process.

Describe the Solvay process.

What percentage of water of crystallization does sodium carbonate
contain ?

What relation does bicarbonate of soda bear to sodium carbonate ?
How is it made ? Explain its use in baking-powders.

What is the substance which is commonly called phosphate of soda t

What is the composition of borax ? Where is it found in nature ?
What change takes place in borax when it is heated ? Explain the
use of borax in soldering. What is meant by saying that borax is an
antiseptic ?

What is water-glass, and how is it made ? What is it used for ?

What action takes place when ammonia is brought together with
acids ? What are the products when hydrochloric, nitric, acd sul-
phuric acids are treated with ammonia ? Why are these substances

QUESTIONS AND PROBLEMS. 259

included among the derivatives of the potassium family ? "What is
the difference between ammonia and ammonium ?

What is sal ammoniac, and how is it chiefly obtained ? Give the
equations expressing the reactions which take place when sal ammo-
niac is treated with caustic soda and with quick- lime.

How is ammonium sulphide made, and what is its composition ?

What relation exists between the atomic weights of the alkali
metals ?

What are flame reactions, and how are they used for the purpose of
detecting substances ?

How can potassium and sodium be detected when both are pres
ent ?

What is a spectrum ? How can the spectrum of a light be used for
telling what substances are in the flame ?

What are the principal parts of the spectroscope ? Of what ser-
vice has it been to chemistry ?

CHAPTER XX.

Mention some of the chief compounds of calcium found in nature.

Of what interest is calcium chloride ? How is it made ?

What is ]ime ? How is it made ? Explain a lime-kiln. Explain
the use of lime in making the lime-light. What change takes place
when lime is left exposed to the air ? What change takes place in it
when it is treated with water ? What is lime water ? What changes
are produced in lime-water by passing carbon dioxide into it V

What is bleaching-powder, and how is it made ? Of what value is
bleaching-powder ? Under what conditions does it give up its chlo-
rine ?

Mention some of the principal varieties of calcium carbonate which
are founl in nature. What are stalagmites and stalactites ?

What is gypsum ? Explain the use of plaster-of -Paris.

Explain the difference between permanent and temporary hardness
of water.

How can temporary hardness be remedied ? How can permanent
hardness be remedied ? Explain the action in each case.

What application is made of gypsum ?

What forms of calcium phosphate are found in nature ? What is
meant by the name normal calcium phosphate ?

Of what importance is calcium phosphate to plants ? What objec-
tion is there to the use of normal calcium phosphate as a fertilizer ?
What is superphosphate of lime, how is it made, and what is it used
for ?

How is mortar made ? Why do freshly-plastered rooms remain
moist so long ? How can the process of drying be hastened ?

What is common glass ? What is the difference between sodium
glass and potassium glass ? What is flint-glass, and for what is it used?

How are colored glasses made ?

Explain how barium dioxide is used for extracting oxygen from,
the air. How is it used in making hydrogen dioxide ?

260 THE ELEMENTS OF CHEMISTRY.

What flame reactions do calcium compounds give ? strontium com
pounds ? barium compounds?

What relation exists between the atomic weights of calcium, stron-
tium, and barium ?

CHAPTER XXI.

Mention the chief compounds of magnesium which are found in
nature.

How is magnesium prepared ? What are its most striking proper
ties ?

What is magnesia? What change does water effect when brought
in contact with magnesia?

Mention the chief forms in which zinc is found in nature,

How is zinc got out of its ores?

What are the most striking properties of zinc?

What is galvanized iron? brass? German silver?

Explain what takes place when zinc is heated to a high tempera-
ture in the air.

What is zinc- white? What advantage has it over lead- white?

What is white vitriol? In what experiments which you have per
formed has it been obtained? How is it made on the large scale ?
What are the final products of roasting zinc sulphide?

Where and in what form does copper chiefly occur in nature ?
What is the substance known as copper pyrites?

What takes place when an oxide of copper is heated with charcoal?
Explain the reaction. What are the most striking properties of cop
per? What takes place when it is heated with nitric acid? with sul-
phuric acid?

Explain the process of copper-plating.

What are alloys? What is brass? bell metal? bronze?

What is the difference ia composition between cuprous and cupric
compounds? Give examples.

What is the composition of cuprous oxide, and what is the name of
that variety of it which occurs in nature?

How is copper oxide made? Explain what takes place when a so-
lution of caustic soda is added to a cold solution of copper sulphate
which is afterwards boiled.

; What is the most common salt of copper? What effect does heat-
Jing produce upon the substance?

In what forms does mercury occur in nature? How is it obtained
from its chief compound? Why are mercury thermometers of no
value in arctic regions?

What are the alloys of mercury called? Why are the zinc plates in
galvanic batteries amalgamated? How is mercuric oxide formed?
For what has it been used in experiments which you have performed?

What is calomel, and how is it obtained? For what is it used?

What is corrosive sublimate, and how is it manufactured? What
objection would there be to having a little corrosive sublimate mixed
with the calomel which is used in medicine?

In what forms does silver occur in nature? Explain how silver is

QUESTION'S AND PROBLEMS. 261

extracted from galenite: (1) by Pattison's process; (2) by the amal-
gamation process.

What action do air and water have upon silver? Why do silver
coins, etc., carried in the pockets become dark-colored? Why do
silver spoons used in eating eggs become tarnished (see near the bot-
tom of page 142)?

Why is not pure silver used in making coins? What is used?

How is silver-plating accomplished? How are mirrors made?

How is silver nitrate made? Why is this salt used in making in-
delible inks? How can stains made by silver nitrate be removed?

Explain all the chemical processes made use of in Experiment 117,
for the purpose of making pure silver nitrate from a silver coin.
Whit change takes place in silver chloride when it is exposed to the
light? in silver bromide? in the iodide?

What example have we already had to deal with which showed
that light can produce chemical changes?

Explain in brief the chemical changes upon which the art of pho-
tography is based.

CHAPTER XXII.

Mention some of the principal compounds of aluminium which
occur in nature.

How is aluminium made?

What are the most important properties of aluminium? How does
its weight compare with that of the metals in common use? What
advantage does it possess over iron?

What are the forms of aluminium oxide found in nature? How
can the oxide be made in the laboratory?

What is ordinary alum? What are the alums? Give examples.
What relation do they bear to sulphuric acid?

What uses are made of alum?

What is the principal silicate containing aluminium? How does
the element potassium get into the soil? Where does clay come from?
Would you expect to find loose soil mostly on the tops of mountains
or in valleys? Why? What is kaoline?

What is porcelain? Explain the process of glazing.

What is ultramarine, and how is it made?

What is aluminium bronze, and how is it made?

Mention the chief compounds of iron which are found in nature.
Where is iron found in the uncombined state?

Explain the process of extracting iron from its ores. What is a flux?
What is slag?

What is pig-iron? cast-iron? wrought-iron ? How is cast-iron con-
verted into wr ought-iron? What is steel? How is steel tempered ?
How is steel made?

What are the properties of pure iron? Explain the change which
iron undergoes in moist air. What is given off when iron is dissolved
in hydrochloric acid?

What is the difference in composition between the ferrous and
ferric compounds? Give the formulas of ferrous and ferric sulphates,

262 THE ELEMENTS OF CHEMISTRY.

ferrous and ferric oxides. How could we decide whether the formula
FeCU or Fe2Cl4 is the correct one for ferrous chloride?

How are ferrous compounds converted into ferric compounds?
Why is the change hastened by adding nitric acid?

How is ferrous chloride made? Explain the changes which take
place when caustic soda is added to its solution, and the mixture is
allowed to stand in contact with the air; when the solution is boiled
aud a few drops of nitric acid added. How can ferric chloride be
converted into ferrous chloride?

What is copperas, and what other names has it? What is it used
for? What are some of the different kinds of ink?

Compare the formula of iron-alum with that of ordinary alum.

What is the principal variety of ferric oxide? What is rouge, and
how is it made? What is the composition of loadstone? Under what
circumstances is this oxide formed?

How is ferrous sulphide made? For what has it been used in ex-
periments already performed?

What is iron pyrites? What changes take place in it when it is
heated in an open vessel ?

In what forms is nickel found in nature? Why is nickel used for
plating other metals and for making coins?

In what forms is cobalt found in nature? What are cobalt com-
pounds principally used for? What is smalt? What is cobalt ultra-
marine?

CHAPTER XXIII. 1/

What is the chief compound of manganese found in nature?
What other compounds with oxygen does manganese form?

What is the chief natural compound of chromium?

What is potassium chromate, and how is it made? What is potas
sium dichromate, and how is it made? Explain the relation which
exists between potassium chromate and potassium dichromate. How
is potassium dichromate converted into potassium chromate?

What takes place when potassium chromate or dichromate is
treated with hydrochloric acid?

What is chrome -yellow? How is it made?

What is chrome-alum? Explain its relation to the other alunu
which have been mentioned.

In what form does the element uranium occur in nature?

In what form does bismuth occur in nature, and how is it obtained
from its ores?

What is fusible metal?

What is formed when bismuth is burned in the air?

What is the chief salt of bismuth ?

CHAPTER XXIV.

1/

In what compounds does lead occur in nature?
How is lead extracted from its ores?

What are the chief properties of lead? Explain the formation of
the " Arbor Saturni."

QUESTION'S AND PROBLEMS. 263

What objection is tbere to the use of lead pipes for conveying
water for drinking purposes? How can lead be detected in water?
What did you learn in Experiment 125 in regard to the action of
water on lead?

What compounds does lead form with oxygen? What takes place
when lead is heated in the air?

What advantage is taken of this fact in separating lead and silver?

What is red lead? What other name has it? What change does
nitric acid effect in it?

What is lead peroxide? What is formed when hydrochloric acid
acts upon lead peroxide?

How could you get the sulphate, chloride, and chromate of lead?

What is white lead? Why does white lead turn black and zinc-
white not?

In what form does tin chiefly occur in nature? How is the metal
obtained from the ore?

What is tin-foil? What effect does air have on tin at the ordinary
temperatures? What effect does nitric acid produce on tin?

What is tin-ware? What danger is there in the use of inferior tin-
ware? What are pins made of?

What is solder? britannia? bronze? bell-metal? Explain the pro-
cess of soldering. What objection is there to the use of solder in
closing tin cans containing things which are to be eaten?

What is the difference in composition between stannous and stannic
compounds?

What is tin salt? What is it used for? What is mosaic gold?

In what form does platinum occur in nature? Where' is it chiefly
found? How is it obtained from its ores?

What are the most striking properties of platinum?

For what purposes is platinum used?

In what form does gold occur in nature?

How is it usually extracted from its ores?

What are its most striking properties?

Why is not pure gold used in making gold ware and coins? What
is 20-carat gold? What is the composition of the standard gold coin
of the United States?

CHAPTER XXV.

What was the first meaning of the name organic chemistry? inor-
ganic chemistry? What does organic chemistry mean now?

Mention some of the principal forms in which carbon occurs in
nature?

What takes place when coal is distilled ?

What takes place when wood is distilled ?

What takes place when bones are distilled?

What is meant in general by fermentation? What is the best
known example of fermentation?

Mention some of the principal classes of compounds of carbon.

How is methyl alcohol formed? What other name has it? What
are its chief properties?

264 THE ELEMENTS OF CHEMISTRY.

How is ordinary alcohol madel Explain what took place in Ex-
periment 128.

What change takes place in sugar when it undergoes fermentation?
What causes the change in the sugar? Why do fruit-juices lose their
sweetness whon exposed to the air?

Mention some other kinds of fermentation besides alcoholic fer-
mentation.

How is alcohol obtained from fermented liquids? What is fusel-
oil?

What are the chief properties of ethyl alcohol?

What are the chief uses of alcohol ?

What is glycerin? How is it obtained? What are its chief proper
ties?

What is formic acid, and where is it found in nature? What are its
chief properties?

What is acetic acid? What is "mother of vinegar "? How is
acetic acid made? Whence come the names pyroligneous acid and
wood- vinegar?

What are the chief properties of acetic acid? For what purposes
is it used? What are the principal salts of acetic acid?

What are the fatty acids? Mention some of the principal fatty
acids. What is such a series as that of the fatty acids called ?

Of what interest is butyric acid? palmitic acid? stearic acid?

What are soaps? How are they made? How does soap act in
washing?

What happens when soap is added to a hard water? Why do the
hands feel sticky when we attempt to wash them in hard water?

What connection is there between soap and civilization? How is
soft-soap made? What connection is there between the manufacture
of sulphuric acid and sodium carbonate and that of soap? What is
the composition of oxalic acid ? Where and in what form is it found
in nature? How is it manufactured ? For what is it used? What is
the composition of lactic acid? How n it formed?

Where is malic acid found in nature? Where is tartaric acid
found in nature?

What is "cream of tartar," and under what circumstances is it
formed?

Where is citric acid found in nature? How is it prepared?

What is ordinary ether? How is it made?

What is meant by the word anaesthetic?

What is the action of an alcohol upon an acid? What is the
product called? What class of substances do the alcohols act like?
Compare the action of nitric acid upon alcohol and upon caustic
potash.

What is meant by saponification?

What are fats? Explain what takes place when fats are treated
with an alkali.

What does butter consist of? oleo-margarin?

What connection is there between the flavors of fruits and ethereal
salts?

What Is nitro-glycerin? To what class of substances does it be-

QUESTIONS AND PBOBLEMS. 265

long? What is dynamite? What relations exist between the hydro-
carbons of the marsh-gas series and the simplest nlcohols and acids?

What is an alcohol ?

What similarity is there between aluminium hydroxide and glycer
in?

What is meant by the expression radical or residue ?

What common acid are the organic acids related to?

CHAPTER XXYI.

What are the carbohydrates?

Where is dextrose found ? What other names has it?

How is dextrose formed? What relation exists between it and cane
sugar? between it and starch?

Describe the process used in the manufacture of glucose.

What are the chief properties of glucose ? How does it differ from
cane-sugar? How can alcohol be obtained from it? How lactic
acid?

What is ievulose? What relation exists between it and cane-sugar7

Where is cane-sugar found in nature?

Describe the process of sugar- refining.

What is molasses? What are the chief properties of sugar? What
is caramel? invert-sugar? What is the action of yeast upon cane-
sugar? What is sugar of milk? What are the constituents of cow's
milk? How is cheese made? What is it? How is sugar of milk
obtained from milk? What does the process of souring of milk con-
sist in ?

Of what importance is cellulose in the vegetable kingdom? What
takes place when cellulose is treated with concentrated sulphuric aci'l
and boiled? What is gun-cotton? collodion? What is collodion used
for? What is celluloid? What is paper? Describe the process of
paper-making.

In what forms is starch found in nature? Describe the manufacture
of starch. What is starch-paste? What change is effected in starch
by dilute acids and ferments?

What are the chief constituents of flour?

What causes bread ' rise?

WhLt is meant by tl name " aromatic compounds "?

What is nitro-benzene, and how is it made?

How is aniline made? What is magenta? What are the aniline
dyes?

What is carbolic acid?

What is the oil of bitter almonds? Where is it found in nature?
What is it used for ?

What is the source of benzoic acid? What are balsams? Give
some examples.

Where is gallic acid found? How is i+ prepared?

Where does tannic acid occur? For what is it used?

What does the process of tanning consist in? In what form antf
where does indigo occur in nature?

266

THE ELEMENTS OF CHE MIST BY.

What is naphthalene? anthracene? What is the chief use of
anthracene?

What is alizarin? How is it made?

What are the giucosides? What examples have already been men-
tioned? Of what importance is myronic acid?

What are the alkaloids? What simple inorganic compound do
they resemble? What is the source of quinine? cocaine? nicotine?
morphine and narcotine?

INDEX.

Acetylene, 108, 109
Acid, acetic, 221

benzoic, 239

boric, 158

bromic, 134

butyric, 222

carbolic, 238

carbonic, 116

chloric, 86, 87

chlorous, 86, 87

chromic, 206

citric, 225

formic, 221

gallic, 239

hydriodic, 135

hydrobromic, 133

hydrochloric, 82

hydrocyanic, 122

hydrofluoric, 135

hypobromous, 134

hypochlorous, 86

lactic, 225

malic, 225

metaphosphoric, 155

metastannic, 212

myronic, 241

nitric, 69

nitrous, 67

oleic, 227

orthophosphoric, 155

oxalic, 224

palmitic, 222

perchloric, 87

phosphoric, 155

propionic, 222

prussic, 122

pyroligneous, 221

silicic, 159

stearic, 282

Acid, sulphuric, 147

sulphurous, 147

tannic, 239

tartaric, 225

tetraboric, 158
Acids, 88, 91, 221, 229

characteristics, 91

dibasic, 151

fatty, 222

monobasic, 151

names of, 92

tribasic, 155
Acid-forming elements, 130
Agate, 160
Air, 20
Alcohol, ethyl, 218

methyl, 218
Alcohols, 218, 228
Alizarin, 241
Alkalies, 88
Alkaloids, 241
Allotropism, 101
Alloys, 188
Allylene, 108
Alum, 197
Aluminium, 196

bronze, 199

hydroxide, 197

oxide, 197

silicates, 198
Alums, 197

Amalgamation process, 192
Amalgams, 190
Amethyst, 160
Amygdann, 239
Ammonia; 67

formation, 65

in air, 20

in gas liquor, 67

268

INDEX.

Ammonium, 174

chloride, 174

salts, 174

sulphide, 175
Analysis, 144
Aniline, 238

dyes, 283
Anthracene, 240
Anthracite coal, 100
Antimony, 158
Apatite, 153
Aqua regia, 73
Aromatic compounds, 237
Arsenic, 155

oxide, 157
Arsine, 156
Asbestos, 185
Atomic theory, 125

weights, 126

determination of, 127
Atoms, 125
Avogadro's law, 126

Baking-powders, 173
Balsams, 239
Barium, 183

dioxide, 184

oxide, 183

sulphate, 139
Bases, 88, 91

names of, 93
Bell metal, 188
Benzene, 108
Benzine, 107
Benzoic aldehyde, 238
Bessemer process, 201
Bicarbonate of s^da, 173
Bismuth, 208

nitrate, 208

oxide, 208
Bituminous coal, 100
Blast furnace, 200
Bleaching, 80

powder, 87, 180
Blow-pipe, compound, 58

oxyhydrogen, 58
Bone oil, 217
Borax, 158, 173
Boron, 158

crystallized, 158

oxide, 158

Brass, 186, 188
Bread-making, 237
Breathing, 26, 113
Britannia, 212
Bromine, 132
Burning in air, 17, 28

in oxygen, 27
Butane, 107
Butylene, 108

Cadmium, 185
Caesium, 177
Calamine, 186
Calcium, 178

carbonate, 180

chloride, 178

fluoride, 178

hydroxide, 179

hypochlorite, 180

oxide, 178

phosphate, 182

sulphate, 181
Calcspar, 130
Calomel, 190
Cane-sugar, 232
Caramel, 233
Carbohydrates, 231
Carbon, 95

as food for plants, 115

dioxide, 110

disulphide, 151

in the air, 114

monoxide, 117
Carbonates, 116
Carbonic acid, 116
Carnelian, 160
Casein, 234
Cast-iron, 200
Celluloid, 235
Cellulose, 234
Cementation, 201
Chalk, 180
Charcoal, 97

animal, 98

reduction by, 104

wcod, 98
Chemical energy, 30

work, 30
Chemistry, 2
Chloride of lime, 180
Chlorine, 77

INDEX.

269

Chlorine acids, 86, 87

bleaching by, 80

comparison with bromine
and iodine, 136

oxides, 87
Chromates, 206
Chrome alum, 207

yellow, 20r
Chromic iron, 206
Chromium, 206
Cinnabar, 190
Clay, 159, 196, 198
Coal, 100
Coal-tar, 110, 217
Cobalt, 205
Cocaine, 242
Coke, 98
Collodion, 235
Combination, chemical, 11
Combining weights, 33
Combustion, 28
Compounds, chemical, 9
Copper, 187

alloys, 188

chlorides, 189

oxides, 189

plating, 188

pyrites, 139, 187

sulphate. 190
Corrosive sublimate, 191
Corundum, 197
Cream of tartar, 173
Cryolite, 135
Cupellation, 192
Cupric compounds, 189
Cuprous compounds, 189
Cyanogen, 122

Deacon's process, 78
Decomposition, 11
Definite proportions, law of, 31
Deliquescent substances, 42
Dextrose, 231
Diamond, 96
Disinfection, 81
Distillation, 61

destructive, 66, 95, 217

of bones, 217

of coal, 100, 217

of wood, 217
Dolomite, 185

Dynamite, 228

Earthenware, 198
Efflorescent substances, 42
Elements, 9, 10

classification, 129

names, 14

symbols, 14
Emery, 197
Epsom salt, 185
Essence of apples, 227

pineapples, 227
Etching, 136
Ethane, 107
Ether, 225
Ethereal salts, 226
Ethers, 225
Ethylene, 108, 109
Eudiometer, 55

Fats, 227
Feldspar, 165, 198
Fermentation, 217, 219
Ferric chloride, 202

oxide, 204
Ferrous chloride, 203

hydroxide, 202

oxide, 202

sulphate, 203
Fire-damp, 108
Flame, 120
Flame-reactions, 175
Flour, 236
Fluorine, 135
Fluor-spar, 135, 178
Flux, 200
Fruit-sugar, 232
Fusel-oil, 220

Galenite, 139, 209
Gallium, 177
Galvanized iron, 186
Gas, olefiant, 109
Gasoline, 107
German silver, 186
Glass, 183
Glauber's salt, 171
Glucose, 231
Glucosides, 238, 241
Gluten, 236

270

INDEX.

Glycerin, 220
Gold, 215
Granite, 196
Grape-sugar, 231
Graphite, 96
Gun-cotton, 235
Gunpowder, 165
Gypsum, 139, 181

Heat and chemical change, 4, 30
Hematite, 199, 204
Heptane, 107
Hexane, 107
Homologous series, 107
Homology, 107
Hydrocarbons, 106
Hydrogen, 45

dioxide, 65

preparation, 45

properties, 48, 49

sulphide, 142
Hypothesis, 124

Illumination, 120
Incense, 239
Indigo, 240
Indium, 177
Inks, 203
Iodine, 134
Iridium, 214
Iron, 199

carbonate, 199

cast, 200

chlorides, 202

oxides, 202

pyrites, 139, 199, 204

Kaoline, 198

Kelp, 134

Kerosene, 107

Kindling temperature, 29

Lactose, 234
Lamp-black, 98
Lapis lazuli, 198
Lead, 209

acetate, 222

carbonate, 212

chromate, 207, 211

oxide, 211

red oxide, 211

Lead, sulphate, 139

sulphide, 209

white, 212
Leblanc's method, 172
Levulose, 232
Lignite, 100
Lime, 179

light, 58
Limestone, 180
Litharge, 211
Lithium, 175

Magenta, 238

Magnesia, 185
Magnesite, 185
Magnesium, 185

carbonate, 185

chloride, 185

oxide, 185

sulphate, 185
Magnetite, 199, 204
Manganese, 206

dioxide, 206

oxides, 206
Marble, 180
Marsh-gas, 108
Marsh's test, 159
Meerschaum, 185
Mercuric chloride, 191
Mercuric oxide, 190
Mercurous chloride, 190
Mercury, 190

chlorides, 190

oxide, 190

sulphide, 190
Metallic properties, 162
Metals, classification, 161
Metathesis, 11
Methane, 107, 108
Mica, 196
Minium, 211
Mixture, mechanical, 9
Molasses, 232
Molecular formulas, 126

weights, 126
Molecules, 126
Morphine, 242
Mortar, 182
Multiple proportions, 35

Naphtha, 107

INDEX.

271

Naphthalene. 240

Narcotine, 242
Neutralization, 88
Nickel, 204
Nicotine, 242
Nitrates, 73
Nitric acid, 67, 69

oxide, 74, 75
Nitrobenzene, 237
Nitrocellulose, 235
Nitrogen, 37

family, 153

in air, 20, 39

oxides, 73

pentoxide, 74

peroxide, 74, 76

trioxide, 74
Nitroglycerin, 227
Nitrous acid, 67

oxide, 74
Nomenclature, acids, 92

bases, 93

salts, 94

Octane, 107

Oil of bitter almonds, 238

Oleo -margarin, 227

Opium, 242

Organic chemistry, 216

Osmium, 214

Oxides, 30

Oxygen, 21

preparation, 21

properties, 24
Oxyhydrogen blow-pipe, 58
Ozone, 64

in air, 65

relation to oxygen, 65

Palladium, 214
Paper, 235
Paraffin, 107
Pattison's process, 191
Pentane, 107
Petroleum, 106
Phenol, 238
Phosphorite, 153
Phosphorus, 153

oxide, 155

red, 154
Photography, 194

Pig iron, 200

Pitchblende, 208

Plaster of Paris, 181

Platinum, 214
chloride, 214

Plumbago, 96

Porcelain, 198

Potash, 165

Potassium, 165

chlorate, 86, 169
chloride, 86
chromate, 206
dichromate, 207
ferrocyanide, 122
hydroxide, 167
hypochlorite, 86
iodide, 166
nitrate, 167

Propane, 107

Propylene, 108

Puddling, 201

Pyroxylin, 234

Quartz, 159, 160 '
Quartzite, 159, 160
Quinine, 241

Radicals, 229

Seduction, 57
Rbchelle salt, 175
Rouge, 204
Eubidium, 177
Ruby, 197

Ruby copper, 187, 189
Rust, 201

Safety-lamp, 121
Safety- matches, 154
Saltpetre, 167
Salts, 91

acid, 151

neutral, 151

nomenclature, 93

normal, 151
Sand, 159
Saponification, 226
Sapphire, 197
Serpentine, 185
Selenium, 152
Siderite, 199
Silica, 159

272

INDEX.

Silicates, 159
Silicon, 159

oxide, 160
Silver, 191

bromide, 194

chloride, 194

iodide, 194

nitrate, 193

plating, 192
Slag, 200
Slaking, 179
Slow oxidation, 26
Soaps, 222
Soapstone, 185
Soda, 171
Sodium, 169

borate, 173

carbonate, 171

chloride, 169

hydroxide, 170

hyposulphite, 195

nitrate, 170

phosphate, 173

sulphate, 171
Solder, 212
Soldering, 173, 213
Solution, 7
Solvay method^ 172
Spectroscope, 176
Spirits of wine, 218
Stalactites, 181
Stalagmites, 181
Stannic compounds, 213
Stannic chloride, 213
Stannic sulphide, 213
Stannous compounds, 213
Stannous chloride, 213
Starch, 236
Stearin, 222
Steel, 201
Stibine, 159
Strontium, 183
Sugar of lead, 222

milk, 234
Sugar- refining, 233
Sulphites, 145
Sulphur, 139

dimorphism of, 141

dioxide, 145

trioxide, 145

Sulphuretted hydrogen, 14$
Superphosphate of lima 182
Symbols, 33, 34, 35

Tannin, 239
Tanning, 240
Tellurium, 152
Tempering, 201
Thallium, 177
Theory, 124
Tin, 212

dichloride, 213

oxide, 212

salt, 213

sulphide, 213

tetrachloride, 213
Tin-stone, 212
Toluene, 108
Turkey-red, 241

Ultramarine, 198
Uranium, 208

Valence, 127
Yerdigris, 222
Vitriol, blue, 190

green, 203

white, 187

Water, 41

analysis, 44
hard, 117, 181, 223
maximum density. 59
of crystallization, 41
as a solvent, 62
synthesis of, 54, 56
uses in chemistry, 62

Water gas, 46, 118

Water-glass, 174

Wei don's process, 78

Wood- spirit, 218

Wood- vinegar, 221

Wrought-iron, 200

Xylene, 108

Zinc, 186

blende, 186
oxide, 186
sulphate, 187

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